diff --git a/src/cli/cli.cpp b/src/cli/cli.cpp
index 45a5fae74..953bfb066 100644
--- a/src/cli/cli.cpp
+++ b/src/cli/cli.cpp
@@ -366,8 +366,8 @@ void Interpreter::ProcessHelp(int argc, char *argv[])
         mServer->OutputFormat("%s\r\n", sCommands[i].mName);
     }
 
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 }
 
 void Interpreter::ProcessAutoStart(int argc, char *argv[])
@@ -470,8 +470,8 @@ exit:
 void Interpreter::ProcessBufferInfo(int argc, char *argv[])
 {
     otBufferInfo bufferInfo;
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 
     otMessageGetBufferInfo(mInstance, &bufferInfo);
 
@@ -914,8 +914,8 @@ void Interpreter::ProcessEidCache(int argc, char *argv[])
     }
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(OT_ERROR_NONE);
 }
 #endif  // OPENTHREAD_FTD
@@ -932,7 +932,7 @@ void Interpreter::ProcessEui64(int argc, char *argv[])
     mServer->OutputFormat("\r\n");
 
 exit:
-    (void)argv;
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(error);
 }
 
@@ -963,8 +963,8 @@ exit:
 void Interpreter::ProcessExit(int argc, char *argv[])
 {
     exit(0);
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 }
 #endif
 
@@ -994,8 +994,8 @@ exit:
 void Interpreter::ProcessFactoryReset(int argc, char *argv[])
 {
     otInstanceFactoryReset(mInstance);
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 }
 
 void Interpreter::ProcessHashMacAddress(int argc, char *argv[])
@@ -1010,7 +1010,7 @@ void Interpreter::ProcessHashMacAddress(int argc, char *argv[])
     mServer->OutputFormat("\r\n");
 
 exit:
-    (void)argv;
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(error);
 }
 
@@ -1264,8 +1264,8 @@ void Interpreter::ProcessLeaderData(int argc, char *argv[])
     mServer->OutputFormat("Leader Router ID: %d\r\n", leaderData.mLeaderRouterId);
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(error);
 }
 
@@ -1465,8 +1465,8 @@ void Interpreter::ProcessNetworkDataRegister(int argc, char *argv[])
     SuccessOrExit(error = otBorderRouterRegister(mInstance));
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(error);
 }
 #endif  // OPENTHREAD_ENABLE_BORDER_ROUTER
@@ -1550,8 +1550,8 @@ void Interpreter::ProcessParent(int argc, char *argv[])
     mServer->OutputFormat("Age: %d\r\n", parentInfo.mAge);
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(error);
 }
 
@@ -1962,7 +1962,7 @@ otError Interpreter::ProcessPrefixRemove(int argc, char *argv[])
     error = otBorderRouterRemoveOnMeshPrefix(mInstance, &prefix);
 
 exit:
-    (void)argc;
+    OT_UNUSED_VARIABLE(argc);
     return error;
 }
 
@@ -2079,16 +2079,16 @@ exit:
 void Interpreter::ProcessReset(int argc, char *argv[])
 {
     otInstanceReset(mInstance);
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 }
 
 void Interpreter::ProcessRloc16(int argc, char *argv[])
 {
     mServer->OutputFormat("%04x\r\n", otThreadGetRloc16(mInstance));
     mServer->OutputFormat("Done\r\n");
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 }
 
 #if OPENTHREAD_ENABLE_BORDER_ROUTER
@@ -2455,8 +2455,8 @@ void Interpreter::ProcessSingleton(int argc, char *argv[])
         mServer->OutputFormat("false\r\n");
     }
 
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 
     AppendResult(error);
 }
@@ -2545,8 +2545,8 @@ void Interpreter::ProcessThread(int argc, char *argv[])
     }
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendResult(error);
 }
 
@@ -2574,8 +2574,8 @@ void Interpreter::ProcessVersion(int argc, char *argv[])
     otStringPtr version(otGetVersionString());
     mServer->OutputFormat("%s\r\n", (const char *)version);
     AppendResult(OT_ERROR_NONE);
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
 }
 
 #if OPENTHREAD_ENABLE_COMMISSIONER && OPENTHREAD_FTD
diff --git a/src/cli/cli_coap.cpp b/src/cli/cli_coap.cpp
index f6dd9386e..5af664956 100644
--- a/src/cli/cli_coap.cpp
+++ b/src/cli/cli_coap.cpp
@@ -341,8 +341,8 @@ void Coap::HandleClientResponse(otCoapHeader *aHeader, otMessage *aMessage, cons
         PrintPayload(aMessage);
     }
 
-    (void)aHeader;
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aHeader);
+    OT_UNUSED_VARIABLE(aMessageInfo);
 }
 
 }  // namespace Cli
diff --git a/src/cli/cli_dataset.cpp b/src/cli/cli_dataset.cpp
index 4fd8cbcec..54445ed52 100644
--- a/src/cli/cli_dataset.cpp
+++ b/src/cli/cli_dataset.cpp
@@ -223,9 +223,9 @@ otError Dataset::ProcessHelp(otInstance *aInstance, int argc, char *argv[])
         sServer->OutputFormat("%s\r\n", sCommands[i].mName);
     }
 
-    (void)aInstance;
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     return OT_ERROR_NONE;
 }
 
@@ -234,8 +234,8 @@ otError Dataset::ProcessActive(otInstance *aInstance, int argc, char *argv[])
     otOperationalDataset dataset;
     otDatasetGetActive(aInstance, &dataset);
 
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     return Print(dataset);
 }
 
@@ -244,8 +244,8 @@ otError Dataset::ProcessPending(otInstance *aInstance, int argc, char *argv[])
     otOperationalDataset dataset;
     otDatasetGetPending(aInstance, &dataset);
 
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     return Print(dataset);
 }
 
@@ -260,7 +260,7 @@ otError Dataset::ProcessActiveTimestamp(otInstance *aInstance, int argc, char *a
     sDataset.mActiveTimestamp = static_cast<uint64_t>(value);
     sDataset.mIsActiveTimestampSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -276,7 +276,7 @@ otError Dataset::ProcessChannel(otInstance *aInstance, int argc, char *argv[])
     sDataset.mChannel = static_cast<uint16_t>(value);
     sDataset.mIsChannelSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -291,7 +291,7 @@ otError Dataset::ProcessChannelMask(otInstance *aInstance, int argc, char *argv[
     SuccessOrExit(error = Interpreter::ParseLong(argv[0], value));
     sDataset.mChannelMaskPage0 = static_cast<uint32_t>(value);
     sDataset.mIsChannelMaskPage0Set = true;
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -300,9 +300,9 @@ exit:
 otError Dataset::ProcessClear(otInstance *aInstance, int argc, char *argv[])
 {
     memset(&sDataset, 0, sizeof(sDataset));
-    (void)aInstance;
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     return OT_ERROR_NONE;
 }
 
@@ -325,7 +325,7 @@ otError Dataset::ProcessCommit(otInstance *aInstance, int argc, char *argv[])
         ExitNow(error = OT_ERROR_PARSE);
     }
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -341,7 +341,7 @@ otError Dataset::ProcessDelay(otInstance *aInstance, int argc, char *argv[])
     sDataset.mDelay = static_cast<uint32_t>(value);
     sDataset.mIsDelaySet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -358,7 +358,7 @@ otError Dataset::ProcessExtPanId(otInstance *aInstance, int argc, char *argv[])
     memcpy(sDataset.mExtendedPanId.m8, extPanId, sizeof(sDataset.mExtendedPanId));
     sDataset.mIsExtendedPanIdSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -376,7 +376,7 @@ otError Dataset::ProcessMasterKey(otInstance *aInstance, int argc, char *argv[])
     memcpy(sDataset.mMasterKey.m8, key, sizeof(sDataset.mMasterKey));
     sDataset.mIsMasterKeySet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -393,7 +393,7 @@ otError Dataset::ProcessMeshLocalPrefix(otInstance *aInstance, int argc, char *a
     memcpy(sDataset.mMeshLocalPrefix.m8, prefix.mFields.m8, sizeof(sDataset.mMeshLocalPrefix.m8));
     sDataset.mIsMeshLocalPrefixSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -411,7 +411,7 @@ otError Dataset::ProcessNetworkName(otInstance *aInstance, int argc, char *argv[
     memcpy(sDataset.mNetworkName.m8, argv[0], length);
     sDataset.mIsNetworkNameSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -427,7 +427,7 @@ otError Dataset::ProcessPanId(otInstance *aInstance, int argc, char *argv[])
     sDataset.mPanId = static_cast<otPanId>(value);
     sDataset.mIsPanIdSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -443,7 +443,7 @@ otError Dataset::ProcessPendingTimestamp(otInstance *aInstance, int argc, char *
     sDataset.mPendingTimestamp = static_cast<uint64_t>(value);
     sDataset.mIsPendingTimestampSet = true;
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -565,7 +565,7 @@ otError Dataset::ProcessMgmtSetCommand(otInstance *aInstance, int argc, char *ar
         ExitNow(error = OT_ERROR_PARSE);
     }
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -661,7 +661,7 @@ otError Dataset::ProcessMgmtGetCommand(otInstance *aInstance, int argc, char *ar
         ExitNow(error = OT_ERROR_PARSE);
     }
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -679,7 +679,7 @@ otError Dataset::ProcessPSKc(otInstance *aInstance, int argc, char *argv[])
                  error = OT_ERROR_PARSE);
 
     sDataset.mIsPSKcSet = true;
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
@@ -729,7 +729,7 @@ otError Dataset::ProcessSecurityPolicy(otInstance *aInstance, int argc, char *ar
     }
 
     sDataset.mIsSecurityPolicySet = true;
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 
 exit:
     return error;
diff --git a/src/cli/cli_uart.cpp b/src/cli/cli_uart.cpp
index f3d859937..177506f63 100644
--- a/src/cli/cli_uart.cpp
+++ b/src/cli/cli_uart.cpp
@@ -251,8 +251,8 @@ void otPlatLog(otLogLevel aLogLevel, otLogRegion aLogRegion, const char *aFormat
     Uart::sUartServer->OutputFormat("\r\n");
     va_end(args);
 
-    (void)aLogLevel;
-    (void)aLogRegion;
+    OT_UNUSED_VARIABLE(aLogLevel);
+    OT_UNUSED_VARIABLE(aLogRegion);
 }
 #ifdef __cplusplus
 }  // extern "C"
diff --git a/src/core/api/instance_api.cpp b/src/core/api/instance_api.cpp
index 2a096e433..469bfdf8f 100644
--- a/src/core/api/instance_api.cpp
+++ b/src/core/api/instance_api.cpp
@@ -222,7 +222,7 @@ otLogLevel otGetDynamicLogLevel(otInstance *aInstance)
     logLevel =  aInstance->mLogLevel;
 #else
     logLevel = static_cast<otLogLevel>(OPENTHREAD_CONFIG_LOG_LEVEL);
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 #endif
 
     return logLevel;
@@ -236,8 +236,8 @@ otError otSetDynamicLogLevel(otInstance *aInstance, otLogLevel aLogLevel)
     aInstance->mLogLevel = aLogLevel;
 #else
     error = OT_ERROR_DISABLED_FEATURE;
-    (void)aInstance;
-    (void)aLogLevel;
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aLogLevel);
 #endif
 
     return error;
diff --git a/src/core/api/link_raw_api.cpp b/src/core/api/link_raw_api.cpp
index 98a05a586..f32fc58b9 100644
--- a/src/core/api/link_raw_api.cpp
+++ b/src/core/api/link_raw_api.cpp
@@ -345,7 +345,7 @@ otError LinkRaw::Transmit(otRadioFrame *aFrame, otLinkRawTransmitDone aCallback)
         mTransmitDoneCallback = aCallback;
 
 #if OPENTHREAD_CONFIG_ENABLE_SOFTWARE_RETRANSMIT
-        (void)aFrame;
+        OT_UNUSED_VARIABLE(aFrame);
         mTransmitAttempts = 0;
         mCsmaAttempts = 0;
 
diff --git a/src/core/api/thread_api.cpp b/src/core/api/thread_api.cpp
index ff33c2934..fcb8033f2 100644
--- a/src/core/api/thread_api.cpp
+++ b/src/core/api/thread_api.cpp
@@ -458,7 +458,7 @@ bool otThreadGetAutoStart(otInstance *aInstance)
 
     return autoStart != 0;
 #else
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
     return false;
 #endif
 }
@@ -469,8 +469,8 @@ otError otThreadSetAutoStart(otInstance *aInstance, bool aStartAutomatically)
     uint8_t autoStart = aStartAutomatically ? 1 : 0;
     return otPlatSettingsSet(aInstance, Settings::kKeyThreadAutoStart, &autoStart, sizeof(autoStart));
 #else
-    (void)aInstance;
-    (void)aStartAutomatically;
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aStartAutomatically);
     return OT_ERROR_NOT_IMPLEMENTED;
 #endif
 }
diff --git a/src/core/api/thread_ftd_api.cpp b/src/core/api/thread_ftd_api.cpp
index 6a87fb093..7cfa92028 100644
--- a/src/core/api/thread_ftd_api.cpp
+++ b/src/core/api/thread_ftd_api.cpp
@@ -244,8 +244,8 @@ otError otThreadSetSteeringData(otInstance *aInstance, otExtAddress *aExtAddress
 #if OPENTHREAD_CONFIG_ENABLE_STEERING_DATA_SET_OOB
     error = aInstance->mThreadNetif.GetMle().SetSteeringData(aExtAddress);
 #else
-    (void)aInstance;
-    (void)aExtAddress;
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aExtAddress);
 
     error = OT_ERROR_DISABLED_FEATURE;
 #endif  // OPENTHREAD_CONFIG_ENABLE_STEERING_DATA_SET_OOB
diff --git a/src/core/coap/coap_secure.cpp b/src/core/coap/coap_secure.cpp
index 848e88efc..eda824715 100644
--- a/src/core/coap/coap_secure.cpp
+++ b/src/core/coap/coap_secure.cpp
@@ -150,7 +150,7 @@ otError CoapSecure::SendMessage(Message &aMessage, const Ip6::MessageInfo &aMess
 
 otError CoapSecure::Send(Message &aMessage, const Ip6::MessageInfo &aMessageInfo)
 {
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     return mNetif.GetDtls().Send(aMessage, aMessage.GetLength());
 }
 
diff --git a/src/core/common/logging.cpp b/src/core/common/logging.cpp
index ad700935a..b94f534a9 100644
--- a/src/core/common/logging.cpp
+++ b/src/core/common/logging.cpp
@@ -108,7 +108,7 @@ static void DumpLine(otInstance *aInstance, otLogLevel aLogLevel, otLogRegion aL
 
     otLogDump("%s", buf);
 
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
 }
 
 void otDump(otInstance *aInstance, otLogLevel aLogLevel, otLogRegion aLogRegion, const char *aId, const void *aBuf,
diff --git a/src/core/common/message.cpp b/src/core/common/message.cpp
index 4aef8a121..2c0864611 100644
--- a/src/core/common/message.cpp
+++ b/src/core/common/message.cpp
@@ -65,8 +65,7 @@ MessagePool::MessagePool(otInstance *aInstance) :
     mNumFreeBuffers = kNumBuffers;
 #endif
 
-    // This is required to remove warning of "unused member variable".
-    (void)mInstance;
+    OT_UNUSED_VARIABLE(mInstance);
 }
 
 Message *MessagePool::New(uint8_t aType, uint16_t aReserved)
@@ -418,7 +417,7 @@ otError Message::Append(const void *aBuf, uint16_t aLength)
     bytesWritten = Write(oldLength, aLength, aBuf);
 
     assert(bytesWritten == (int)aLength);
-    (void)bytesWritten;
+    OT_UNUSED_VARIABLE(bytesWritten);
 
 exit:
     return error;
diff --git a/src/core/mac/mac.cpp b/src/core/mac/mac.cpp
index bf64528f6..24f0fdf92 100644
--- a/src/core/mac/mac.cpp
+++ b/src/core/mac/mac.cpp
@@ -286,7 +286,7 @@ otError Mac::ConvertBeaconToActiveScanResult(Frame *aBeaconFrame, otActiveScanRe
 
     otLogInfoMac(GetInstance(), "Received Beacon, %s", beaconPayload->ToInfoString(stringBuffer, sizeof(stringBuffer)));
 
-    (void)stringBuffer;
+    OT_UNUSED_VARIABLE(stringBuffer);
 
 exit:
     return error;
@@ -684,7 +684,7 @@ void Mac::SendBeacon(Frame &aFrame)
 
     otLogInfoMac(GetInstance(), "Sending Beacon, %s", beaconPayload->ToInfoString(stringBuffer, sizeof(stringBuffer)));
 
-    (void)stringBuffer;
+    OT_UNUSED_VARIABLE(stringBuffer);
 }
 
 void Mac::ProcessTransmitSecurity(Frame &aFrame)
@@ -1169,7 +1169,7 @@ void Mac::SentFrame(otError aError)
             ExitNow();
         }
 
-        (void)stringBuffer;
+        OT_UNUSED_VARIABLE(stringBuffer);
         break;
     }
 
@@ -1622,7 +1622,7 @@ exit:
             otLogInfoMac(GetInstance(), "Frame rx failed, error:%s, %s", otThreadErrorToString(error),
                          aFrame->ToInfoString(stringBuffer, sizeof(stringBuffer)));
 
-            (void)stringBuffer;
+            OT_UNUSED_VARIABLE(stringBuffer);
         }
 
         switch (error)
diff --git a/src/core/meshcop/commissioner.cpp b/src/core/meshcop/commissioner.cpp
index fbb8993e6..9d299431d 100644
--- a/src/core/meshcop/commissioner.cpp
+++ b/src/core/meshcop/commissioner.cpp
@@ -842,7 +842,7 @@ void Commissioner::HandleRelayReceive(Coap::Header &aHeader, Message &aMessage,
     mNetif.GetCoapSecure().Receive(aMessage, joinerMessageInfo);
 
 exit:
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     otLogFuncExit();
 }
 
@@ -861,7 +861,7 @@ void Commissioner::HandleDatasetChanged(Coap::Header &aHeader, Message &aMessage
                  aHeader.GetCode() == OT_COAP_CODE_POST);
 
     otLogInfoMeshCoP(GetInstance(), "received dataset changed");
-    (void)aMessage;
+    OT_UNUSED_VARIABLE(aMessage);
 
     SuccessOrExit(mNetif.GetCoap().SendEmptyAck(aHeader, aMessageInfo));
 
@@ -881,7 +881,7 @@ void Commissioner::HandleJoinerFinalize(void *aContext, otCoapHeader *aHeader, o
 
 void Commissioner::HandleJoinerFinalize(Coap::Header &aHeader, Message &aMessage, const Ip6::MessageInfo &aMessageInfo)
 {
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     StateTlv::State state = StateTlv::kAccept;
     ProvisioningUrlTlv provisioningUrl;
 
@@ -974,7 +974,7 @@ otError Commissioner::SendRelayTransmit(void *aContext, Message &aMessage, const
 
 otError Commissioner::SendRelayTransmit(Message &aMessage, const Ip6::MessageInfo &aMessageInfo)
 {
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     otError error = OT_ERROR_NONE;
     Coap::Header header;
     JoinerUdpPortTlv udpPort;
diff --git a/src/core/meshcop/dtls.cpp b/src/core/meshcop/dtls.cpp
index ac3aa7b8e..64e88c800 100644
--- a/src/core/meshcop/dtls.cpp
+++ b/src/core/meshcop/dtls.cpp
@@ -370,7 +370,7 @@ int Dtls::HandleMbedtlsExportKeys(const unsigned char *aMasterSecret, const unsi
 
     otLogInfoMeshCoP(GetInstance(), "Generated KEK");
 
-    (void)aMasterSecret;
+    OT_UNUSED_VARIABLE(aMasterSecret);
     return 0;
 }
 
diff --git a/src/core/meshcop/joiner_router.cpp b/src/core/meshcop/joiner_router.cpp
index 3cffb0edc..c01ecc747 100644
--- a/src/core/meshcop/joiner_router.cpp
+++ b/src/core/meshcop/joiner_router.cpp
@@ -303,7 +303,7 @@ void JoinerRouter::HandleRelayTransmit(Coap::Header &aHeader, Message &aMessage,
     }
 
 exit:
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 
     if (error != OT_ERROR_NONE && message != NULL)
     {
@@ -513,7 +513,7 @@ void JoinerRouter::HandleJoinerEntrustResponse(void *aContext, otCoapHeader *aHe
 void JoinerRouter::HandleJoinerEntrustResponse(Coap::Header *aHeader, Message *aMessage,
                                                const Ip6::MessageInfo *aMessageInfo, otError aResult)
 {
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 
     mExpectJoinEntRsp = false;
     SendDelayedJoinerEntrust();
diff --git a/src/core/meshcop/leader.cpp b/src/core/meshcop/leader.cpp
index ed38d2f0f..69d173f79 100644
--- a/src/core/meshcop/leader.cpp
+++ b/src/core/meshcop/leader.cpp
@@ -117,7 +117,7 @@ void Leader::HandlePetition(Coap::Header &aHeader, Message &aMessage, const Ip6:
     mTimer.Start(Timer::SecToMsec(kTimeoutLeaderPetition));
 
 exit:
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     SendPetitionResponse(aHeader, aMessageInfo, state);
 }
 
diff --git a/src/core/net/dhcp6_client.cpp b/src/core/net/dhcp6_client.cpp
index 6f28d39b3..0b371338a 100644
--- a/src/core/net/dhcp6_client.cpp
+++ b/src/core/net/dhcp6_client.cpp
@@ -84,7 +84,7 @@ otInstance *Dhcp6Client::GetInstance(void)
 void Dhcp6Client::UpdateAddresses(otInstance *aInstance, otDhcpAddress *aAddresses, uint32_t aNumAddresses,
                                   void *aContext)
 {
-    (void)aContext;
+    OT_UNUSED_VARIABLE(aContext);
     bool found = false;
     bool newAgent = false;
     otDhcpAddress *address = NULL;
@@ -529,7 +529,7 @@ void Dhcp6Client::HandleUdpReceive(void *aContext, otMessage *aMessage, const ot
 void Dhcp6Client::HandleUdpReceive(Message &aMessage, const Ip6::MessageInfo &aMessageInfo)
 {
     Dhcp6Header header;
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 
     VerifyOrExit(aMessage.Read(aMessage.GetOffset(), sizeof(header), &header) == sizeof(header));
     aMessage.MoveOffset(sizeof(header));
diff --git a/src/core/net/dns_client.cpp b/src/core/net/dns_client.cpp
index b0333f95d..e40654efa 100644
--- a/src/core/net/dns_client.cpp
+++ b/src/core/net/dns_client.cpp
@@ -460,7 +460,7 @@ void Client::HandleUdpReceive(Message &aMessage, const Ip6::MessageInfo &aMessag
 
     // RFC1035 7.3. Resolver cannot rely that a response will come from the same address
     // which it sent the corresponding query to.
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 
     VerifyOrExit(aMessage.Read(aMessage.GetOffset(), sizeof(responseHeader), &responseHeader) ==
                  sizeof(responseHeader));
diff --git a/src/core/thread/address_resolver.cpp b/src/core/thread/address_resolver.cpp
index 0a2ac09d4..e41569be4 100644
--- a/src/core/thread/address_resolver.cpp
+++ b/src/core/thread/address_resolver.cpp
@@ -669,7 +669,7 @@ void AddressResolver::HandleIcmpReceive(void *aContext, otMessage *aMessage, con
                                                                 *static_cast<const Ip6::MessageInfo *>(aMessageInfo),
                                                                 *static_cast<const Ip6::IcmpHeader *>(aIcmpHeader));
 
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 }
 
 void AddressResolver::HandleIcmpReceive(Message &aMessage, const Ip6::MessageInfo &aMessageInfo,
@@ -692,7 +692,7 @@ void AddressResolver::HandleIcmpReceive(Message &aMessage, const Ip6::MessageInf
     }
 
 exit:
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 }
 
 }  // namespace ot
diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index b8df4ce75..be8a9b2e1 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -1783,7 +1783,7 @@ exit:
         otLogInfoMac(GetInstance(), "Dropping rx frame, error:%s, %s", otThreadErrorToString(error),
                      aFrame.ToInfoString(stringBuffer, sizeof(stringBuffer)));
 
-        (void)stringBuffer;
+        OT_UNUSED_VARIABLE(stringBuffer);
     }
 }
 
@@ -1859,7 +1859,7 @@ exit:
             aMessageInfo.mLinkSecurity ? "yes" : "no"
         );
 
-        (void)srcStringBuffer;
+        OT_UNUSED_VARIABLE(srcStringBuffer);
 
         if (message != NULL)
         {
@@ -2014,8 +2014,8 @@ exit:
         char srcStringBuffer[Mac::Address::kAddressStringSize];
         char dstStringBuffer[Mac::Address::kAddressStringSize];
 
-        (void)srcStringBuffer;
-        (void)dstStringBuffer;
+        OT_UNUSED_VARIABLE(srcStringBuffer);
+        OT_UNUSED_VARIABLE(dstStringBuffer);
 
         otLogInfoMac(
             GetInstance(),
@@ -2126,8 +2126,8 @@ exit:
         char srcStringBuffer[Mac::Address::kAddressStringSize];
         char dstStringBuffer[Mac::Address::kAddressStringSize];
 
-        (void)srcStringBuffer;
-        (void)dstStringBuffer;
+        OT_UNUSED_VARIABLE(srcStringBuffer);
+        OT_UNUSED_VARIABLE(dstStringBuffer);
 
         otLogInfoMac(
             GetInstance(),
diff --git a/src/core/thread/mle.cpp b/src/core/thread/mle.cpp
index 60d22e12b..4407ec2d8 100644
--- a/src/core/thread/mle.cpp
+++ b/src/core/thread/mle.cpp
@@ -2489,7 +2489,7 @@ otError Mle::HandleLeaderData(const Message &aMessage, const Ip6::MessageInfo &a
 
 exit:
 
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
 
     if (dataRequest)
     {
@@ -2814,7 +2814,7 @@ exit:
         otLogWarnMleErr(GetInstance(), error, "Failed to process Child ID Response");
     }
 
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     return error;
 }
 
@@ -3040,7 +3040,7 @@ otError Mle::HandleAnnounce(const Message &aMessage, const Ip6::MessageInfo &aMe
     }
 
 exit:
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aMessageInfo);
     return error;
 }
 
@@ -3216,7 +3216,7 @@ Neighbor *Mle::GetNeighbor(const Mac::Address &aAddress)
 
 uint16_t Mle::GetNextHop(uint16_t aDestination) const
 {
-    (void)aDestination;
+    OT_UNUSED_VARIABLE(aDestination);
     return (mParent.GetState() == Neighbor::kStateValid) ? mParent.GetRloc16() : static_cast<uint16_t>
            (Mac::kShortAddrInvalid);
 }
diff --git a/src/core/thread/mle.hpp b/src/core/thread/mle.hpp
index 3be370370..48c5b4019 100644
--- a/src/core/thread/mle.hpp
+++ b/src/core/thread/mle.hpp
@@ -1209,7 +1209,7 @@ protected:
      * @returns A pointer to the neighbor object.
      *
      */
-    Neighbor *GetNeighbor(const Ip6::Address &aAddress) { (void)aAddress; return NULL; }
+    Neighbor *GetNeighbor(const Ip6::Address &aAddress) { OT_UNUSED_VARIABLE(aAddress); return NULL; }
 
     /**
      * This method returns the next hop towards an RLOC16 destination.
diff --git a/src/core/thread/mle_router.cpp b/src/core/thread/mle_router.cpp
index c47d00627..d2eea8dff 100644
--- a/src/core/thread/mle_router.cpp
+++ b/src/core/thread/mle_router.cpp
@@ -2033,7 +2033,7 @@ otError MleRouter::UpdateChildAddresses(const AddressRegistrationTlv &aTlv, Chil
                      (count == 1) ? "" : "es");
     }
 
-    (void)stringBuffer;
+    OT_UNUSED_VARIABLE(stringBuffer);
 
     return OT_ERROR_NONE;
 }
@@ -3886,8 +3886,8 @@ void MleRouter::HandleAddressSolicitResponse(void *aContext, otCoapHeader *aHead
 void MleRouter::HandleAddressSolicitResponse(Coap::Header *aHeader, Message *aMessage,
                                              const Ip6::MessageInfo *aMessageInfo, otError aResult)
 {
-    (void)aResult;
-    (void)aMessageInfo;
+    OT_UNUSED_VARIABLE(aResult);
+    OT_UNUSED_VARIABLE(aMessageInfo);
 
     ThreadStatusTlv statusTlv;
     ThreadRloc16Tlv rlocTlv;
diff --git a/src/core/thread/mle_router_mtd.hpp b/src/core/thread/mle_router_mtd.hpp
index c3abc144a..62d90148e 100644
--- a/src/core/thread/mle_router_mtd.hpp
+++ b/src/core/thread/mle_router_mtd.hpp
@@ -146,7 +146,7 @@ private:
     otError HandleDiscoveryRequest(const Message &, const Ip6::MessageInfo &) { return OT_ERROR_DROP; }
 
     void StopAdvertiseTimer(void) { }
-    otError ProcessRouteTlv(const RouteTlv &aRoute) { (void)aRoute; return OT_ERROR_NONE; }
+    otError ProcessRouteTlv(const RouteTlv &aRoute) { OT_UNUSED_VARIABLE(aRoute); return OT_ERROR_NONE; }
 };
 
 }  // namespace Mle
diff --git a/src/core/thread/network_data_leader_ftd.cpp b/src/core/thread/network_data_leader_ftd.cpp
index a0f9f0bdf..a32783bf8 100644
--- a/src/core/thread/network_data_leader_ftd.cpp
+++ b/src/core/thread/network_data_leader_ftd.cpp
@@ -541,7 +541,7 @@ bool Leader::IsStableUpdated(uint16_t aRloc16, uint8_t *aTlvs, uint8_t aTlvsLeng
     }
 
 exit:
-    (void)aRloc16;
+    OT_UNUSED_VARIABLE(aRloc16);
     return rval;
 }
 
diff --git a/src/core/thread/thread_netif.cpp b/src/core/thread/thread_netif.cpp
index d57bc2365..d314964c3 100644
--- a/src/core/thread/thread_netif.cpp
+++ b/src/core/thread/thread_netif.cpp
@@ -195,7 +195,7 @@ otError ThreadNetif::TmfFilter(const Message &aMessage, const Ip6::MessageInfo &
                  (aMessageInfo.GetSockAddr().IsLinkLocal() && aMessageInfo.GetPeerAddr().IsLinkLocal()),
                  error = OT_ERROR_NOT_TMF);
 exit:
-    (void)aMessage;
+    OT_UNUSED_VARIABLE(aMessage);
     return error;
 }
 
diff --git a/src/diag/diag_process.cpp b/src/diag/diag_process.cpp
index 6161732c8..2f5e3a898 100644
--- a/src/diag/diag_process.cpp
+++ b/src/diag/diag_process.cpp
@@ -149,8 +149,8 @@ void Diag::ProcessStart(int argc, char *argv[], char *aOutput, size_t aOutputMax
     snprintf(aOutput, aOutputMaxLen, "start diagnostics mode\r\nstatus 0x%02x\r\n", error);
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendErrorResult(error, aOutput, aOutputMaxLen);
 }
 
@@ -169,8 +169,8 @@ void Diag::ProcessStop(int argc, char *argv[], char *aOutput, size_t aOutputMaxL
             static_cast<int>(sStats.first_lqi), error);
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendErrorResult(error, aOutput, aOutputMaxLen);
 }
 
@@ -314,8 +314,8 @@ void Diag::ProcessSleep(int argc, char *argv[], char *aOutput, size_t aOutputMax
     snprintf(aOutput, aOutputMaxLen, "sleeping now...\r\n");
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendErrorResult(error, aOutput, aOutputMaxLen);
 }
 
@@ -330,14 +330,14 @@ void Diag::ProcessStats(int argc, char *argv[], char *aOutput, size_t aOutputMax
             static_cast<int>(sStats.first_rssi), static_cast<int>(sStats.first_lqi));
 
 exit:
-    (void)argc;
-    (void)argv;
+    OT_UNUSED_VARIABLE(argc);
+    OT_UNUSED_VARIABLE(argv);
     AppendErrorResult(error, aOutput, aOutputMaxLen);
 }
 
 void Diag::DiagTransmitDone(otInstance *aInstance, otError aError)
 {
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
     if (aError == OT_ERROR_NONE)
     {
         sStats.sent_packets++;
@@ -356,7 +356,7 @@ void Diag::DiagTransmitDone(otInstance *aInstance, otError aError)
 
 void Diag::DiagReceiveDone(otInstance *aInstance, otRadioFrame *aFrame, otError aError)
 {
-    (void)aInstance;
+    OT_UNUSED_VARIABLE(aInstance);
     if (aError == OT_ERROR_NONE)
     {
         // for sensitivity test, only record the rssi and lqi for the first packet
@@ -394,7 +394,7 @@ extern "C" void otPlatDiagAlarmFired(otInstance *aInstance)
 
 extern "C" void otPlatDiagRadioTransmitDone(otInstance *aInstance, otRadioFrame *aFrame, otError aError)
 {
-    (void)aFrame;
+    OT_UNUSED_VARIABLE(aFrame);
 
     Diag::DiagTransmitDone(aInstance, aError);
 }
diff --git a/src/ncp/ncp_base.cpp b/src/ncp/ncp_base.cpp
index bed028f99..cb2b3f206 100644
--- a/src/ncp/ncp_base.cpp
+++ b/src/ncp/ncp_base.cpp
@@ -1467,7 +1467,7 @@ void NcpBase::HandleReceive(const uint8_t *aBuf, uint16_t aBufLength)
 void NcpBase::HandleFrameRemovedFromNcpBuffer(void *aContext, NcpFrameBuffer::FrameTag aFrameTag,
                                               NcpFrameBuffer *aNcpBuffer)
 {
-    (void)aNcpBuffer;
+    OT_UNUSED_VARIABLE(aNcpBuffer);
     static_cast<NcpBase *>(aContext)->HandleFrameRemovedFromNcpBuffer(aFrameTag);
 }
 
@@ -1833,9 +1833,9 @@ otError NcpBase::OutboundFrameFeedPacked(const char *aPackFormat, ...)
 
 otError NcpBase::CommandHandler_NOOP(uint8_t aHeader, unsigned int aCommand, const uint8_t *aArgPtr, uint16_t aArgLen)
 {
-    (void)aCommand;
-    (void)aArgPtr;
-    (void)aArgLen;
+    OT_UNUSED_VARIABLE(aCommand);
+    OT_UNUSED_VARIABLE(aArgPtr);
+    OT_UNUSED_VARIABLE(aArgLen);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_OK);
 }
@@ -1846,10 +1846,10 @@ otError NcpBase::CommandHandler_RESET(uint8_t aHeader, unsigned int aCommand, co
     otError error = OT_ERROR_NONE;
 
     // We aren't using any of the arguments to this function.
-    (void)aHeader;
-    (void)aCommand;
-    (void)aArgPtr;
-    (void)aArgLen;
+    OT_UNUSED_VARIABLE(aHeader);
+    OT_UNUSED_VARIABLE(aCommand);
+    OT_UNUSED_VARIABLE(aArgPtr);
+    OT_UNUSED_VARIABLE(aArgLen);
 
     // Signal a platform reset. If implemented, this function
     // shouldn't return.
@@ -1891,7 +1891,7 @@ otError NcpBase::CommandHandler_PROP_VALUE_GET(uint8_t aHeader, unsigned int aCo
         error = SendLastStatus(aHeader, SPINEL_STATUS_PARSE_ERROR);
     }
 
-    (void)aCommand;
+    OT_UNUSED_VARIABLE(aCommand);
 
     return error;
 }
@@ -1928,7 +1928,7 @@ otError NcpBase::CommandHandler_PROP_VALUE_SET(uint8_t aHeader, unsigned int aCo
         error = SendLastStatus(aHeader, SPINEL_STATUS_PARSE_ERROR);
     }
 
-    (void)aCommand;
+    OT_UNUSED_VARIABLE(aCommand);
 
     return error;
 }
@@ -1965,7 +1965,7 @@ otError NcpBase::CommandHandler_PROP_VALUE_INSERT(uint8_t aHeader, unsigned int
         error = SendLastStatus(aHeader, SPINEL_STATUS_PARSE_ERROR);
     }
 
-    (void)aCommand;
+    OT_UNUSED_VARIABLE(aCommand);
 
     return error;
 }
@@ -2002,7 +2002,7 @@ otError NcpBase::CommandHandler_PROP_VALUE_REMOVE(uint8_t aHeader, unsigned int
         error = SendLastStatus(aHeader, SPINEL_STATUS_PARSE_ERROR);
     }
 
-    (void)aCommand;
+    OT_UNUSED_VARIABLE(aCommand);
 
     return error;
 }
@@ -2010,9 +2010,9 @@ otError NcpBase::CommandHandler_PROP_VALUE_REMOVE(uint8_t aHeader, unsigned int
 otError NcpBase::CommandHandler_NET_SAVE(uint8_t aHeader, unsigned int aCommand, const uint8_t *aArgPtr,
                                          uint16_t aArgLen)
 {
-    (void)aCommand;
-    (void)aArgPtr;
-    (void)aArgLen;
+    OT_UNUSED_VARIABLE(aCommand);
+    OT_UNUSED_VARIABLE(aArgPtr);
+    OT_UNUSED_VARIABLE(aArgLen);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_UNIMPLEMENTED);
 }
@@ -2020,9 +2020,9 @@ otError NcpBase::CommandHandler_NET_SAVE(uint8_t aHeader, unsigned int aCommand,
 otError NcpBase::CommandHandler_NET_CLEAR(uint8_t aHeader, unsigned int aCommand, const uint8_t *aArgPtr,
                                           uint16_t aArgLen)
 {
-    (void)aCommand;
-    (void)aArgPtr;
-    (void)aArgLen;
+    OT_UNUSED_VARIABLE(aCommand);
+    OT_UNUSED_VARIABLE(aArgPtr);
+    OT_UNUSED_VARIABLE(aArgLen);
 
     return SendLastStatus(aHeader, ThreadErrorToSpinelStatus(otInstanceErasePersistentInfo(mInstance)));
 }
@@ -2030,9 +2030,9 @@ otError NcpBase::CommandHandler_NET_CLEAR(uint8_t aHeader, unsigned int aCommand
 otError NcpBase::CommandHandler_NET_RECALL(uint8_t aHeader, unsigned int aCommand, const uint8_t *aArgPtr,
                                            uint16_t aArgLen)
 {
-    (void)aCommand;
-    (void)aArgPtr;
-    (void)aArgLen;
+    OT_UNUSED_VARIABLE(aCommand);
+    OT_UNUSED_VARIABLE(aArgPtr);
+    OT_UNUSED_VARIABLE(aArgLen);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_UNIMPLEMENTED);
 }
@@ -2089,7 +2089,7 @@ exit:
         error = SendLastStatus(aHeader, spinelError);
     }
 
-    (void)aCommand;
+    OT_UNUSED_VARIABLE(aCommand);
 
     return error;
 }
@@ -2133,7 +2133,7 @@ otError NcpBase::CommandHandler_POKE(uint8_t aHeader, unsigned int aCommand, con
 exit:
     error = SendLastStatus(aHeader, spinelError);
 
-    (void)aCommand;
+    OT_UNUSED_VARIABLE(aCommand);
 
     return error;
 }
@@ -2299,7 +2299,7 @@ otError NcpBase::GetPropertyHandler_HWADDR(uint8_t aHeader, spinel_prop_key_t aK
 otError NcpBase::GetPropertyHandler_LOCK(uint8_t aHeader, spinel_prop_key_t aKey)
 {
     // TODO: Implement property lock (Needs API!)
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_UNIMPLEMENTED);
 }
@@ -3364,7 +3364,7 @@ exit:
 otError NcpBase::GetPropertyHandler_IPV6_ROUTE_TABLE(uint8_t aHeader, spinel_prop_key_t aKey)
 {
     // TODO: Implement get route table
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_UNIMPLEMENTED);
 }
@@ -3463,7 +3463,7 @@ exit:
 otError NcpBase::GetPropertyHandler_STREAM_NET(uint8_t aHeader, spinel_prop_key_t aKey)
 {
     // TODO: Implement explicit data poll.
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_UNIMPLEMENTED);
 }
@@ -4247,9 +4247,9 @@ otError NcpBase::SetPropertyHandler_POWER_STATE(uint8_t aHeader, spinel_prop_key
                                                 uint16_t aValueLen)
 {
     // TODO: Implement POWER_STATE
-    (void)aKey;
-    (void)aValuePtr;
-    (void)aValueLen;
+    OT_UNUSED_VARIABLE(aKey);
+    OT_UNUSED_VARIABLE(aValuePtr);
+    OT_UNUSED_VARIABLE(aValueLen);
 
     return SendLastStatus(aHeader, SPINEL_STATUS_UNIMPLEMENTED);
 }
@@ -4822,7 +4822,7 @@ exit:
         error = SendLastStatus(aHeader, ThreadErrorToSpinelStatus(error));
     }
 
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return error;
 }
@@ -5152,7 +5152,7 @@ exit:
         error = SendLastStatus(aHeader, ThreadErrorToSpinelStatus(error));
     }
 
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return error;
 }
@@ -5219,7 +5219,7 @@ exit:
         error = SendLastStatus(aHeader, ThreadErrorToSpinelStatus(error));
     }
 
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return error;
 }
@@ -5601,7 +5601,7 @@ otError NcpBase::SetPropertyHandler_CNTR_RESET(uint8_t aHeader, spinel_prop_key_
     error = OT_ERROR_NOT_IMPLEMENTED;
 
 exit:
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     // There is currently no getter for PROP_CNTR_RESET, so we just
     // return SPINEL_STATUS_OK for success when the counters are reset.
@@ -5638,7 +5638,7 @@ otError NcpBase::SetPropertyHandler_THREAD_COMMISSIONER_ENABLED(uint8_t aHeader,
     }
 
 exit:
-    (void)aKey;
+    OT_UNUSED_VARIABLE(aKey);
 
     return SendLastStatus(aHeader, ThreadErrorToSpinelStatus(error));
 }
@@ -7490,8 +7490,8 @@ otError otNcpRegisterPeekPokeDelagates(otNcpDelegateAllowPeekPoke aAllowPeekDele
         ncp->RegisterPeekPokeDelagates(aAllowPeekDelegate, aAllowPokeDelegate);
     }
 #else
-    (void)aAllowPeekDelegate;
-    (void)aAllowPokeDelegate;
+    OT_UNUSED_VARIABLE(aAllowPeekDelegate);
+    OT_UNUSED_VARIABLE(aAllowPokeDelegate);
 
     error = OT_ERROR_DISABLED_FEATURE;
 
@@ -7515,7 +7515,7 @@ void otNcpRegisterLegacyHandlers(const otNcpLegacyHandlers *aHandlers)
     }
 
 #else
-    (void)aHandlers;
+    OT_UNUSED_VARIABLE(aHandlers);
 #endif
 }
 
@@ -7530,7 +7530,7 @@ void otNcpHandleDidReceiveNewLegacyUlaPrefix(const uint8_t *aUlaPrefix)
     }
 
 #else
-    (void)aUlaPrefix;
+    OT_UNUSED_VARIABLE(aUlaPrefix);
 #endif
 }
 
@@ -7545,6 +7545,6 @@ void otNcpHandleLegacyNodeDidJoin(const otExtAddress *aExtAddr)
     }
 
 #else
-    (void)aExtAddr;
+    OT_UNUSED_VARIABLE(aExtAddr);
 #endif
 }
diff --git a/src/ncp/ncp_spi.cpp b/src/ncp/ncp_spi.cpp
index 93ea2ad76..f1f296bca 100644
--- a/src/ncp/ncp_spi.cpp
+++ b/src/ncp/ncp_spi.cpp
@@ -248,8 +248,8 @@ void NcpSpi::SpiTransactionProcess(void)
 
 void NcpSpi::HandleFrameAddedToTxBuffer(void *aContext, NcpFrameBuffer::FrameTag aTag, NcpFrameBuffer *aNcpFrameBuffer)
 {
-    (void)aNcpFrameBuffer;
-    (void)aTag;
+    OT_UNUSED_VARIABLE(aNcpFrameBuffer);
+    OT_UNUSED_VARIABLE(aTag);
 
     static_cast<NcpSpi *>(aContext)->mPrepareTxFrameTask.Post();
 }
diff --git a/src/ncp/ncp_uart.cpp b/src/ncp/ncp_uart.cpp
index 7c834dbb7..b99190b20 100644
--- a/src/ncp/ncp_uart.cpp
+++ b/src/ncp/ncp_uart.cpp
@@ -108,8 +108,8 @@ NcpUart::NcpUart(otInstance *aInstance):
 void NcpUart::HandleFrameAddedToNcpBuffer(void *aContext, NcpFrameBuffer::FrameTag aTag,
                                           NcpFrameBuffer *aNcpFrameBuffer)
 {
-    (void)aNcpFrameBuffer;
-    (void)aTag;
+    OT_UNUSED_VARIABLE(aNcpFrameBuffer);
+    OT_UNUSED_VARIABLE(aTag);
 
     static_cast<NcpUart *>(aContext)->HandleFrameAddedToNcpBuffer();
 }
@@ -293,8 +293,8 @@ void otPlatLog(otLogLevel aLogLevel, otLogRegion aLogRegion, const char *aFormat
 
     va_end(args);
 
-    (void)aLogLevel;
-    (void)aLogRegion;
+    OT_UNUSED_VARIABLE(aLogLevel);
+    OT_UNUSED_VARIABLE(aLogRegion);
 }
 #ifdef __cplusplus
 }  // extern "C"