diff --git a/src/core/common/instance.cpp b/src/core/common/instance.cpp
index b849b3fdb..a4bae2d8b 100644
--- a/src/core/common/instance.cpp
+++ b/src/core/common/instance.cpp
@@ -51,17 +51,26 @@ otDEFINE_ALIGNED_VAR(gInstanceRaw, sizeof(Instance), uint64_t);
 #endif
 
 Instance::Instance(void)
-    : mTimerMilliScheduler(*this)
+    : mTaskletScheduler()
+    , mTimerMilliScheduler(*this)
 #if OPENTHREAD_CONFIG_ENABLE_PLATFORM_USEC_TIMER
     , mTimerMicroScheduler(*this)
 #endif
 #if OPENTHREAD_MTD || OPENTHREAD_FTD
+#if !OPENTHREAD_ENABLE_MULTIPLE_INSTANCES
+    , mHeap()
+#endif
+    , mMbedTls()
+#endif // #if OPENTHREAD_MTD || OPENTHREAD_FTD
+    , mRandomManager()
+#if OPENTHREAD_MTD || OPENTHREAD_FTD
+    , mNotifier(*this)
+    , mSettings(*this)
+    , mMessagePool(*this)
     , mActiveScanCallback(NULL)
     , mActiveScanCallbackContext(NULL)
     , mEnergyScanCallback(NULL)
     , mEnergyScanCallbackContext(NULL)
-    , mNotifier(*this)
-    , mSettings(*this)
     , mIp6(*this)
     , mThreadNetif(*this)
 #if OPENTHREAD_ENABLE_APPLICATION_COAP
@@ -79,11 +88,10 @@ Instance::Instance(void)
 #if OPENTHREAD_CONFIG_ENABLE_ANNOUNCE_SENDER
     , mAnnounceSender(*this)
 #endif
-    , mMessagePool(*this)
 #endif // OPENTHREAD_MTD || OPENTHREAD_FTD
 #if OPENTHREAD_RADIO || OPENTHREAD_ENABLE_RAW_LINK_API
     , mLinkRaw(*this)
-#endif // OPENTHREAD_RADIO || OPENTHREAD_ENABLE_RAW_LINK_API
+#endif
 #if OPENTHREAD_CONFIG_ENABLE_DYNAMIC_LOG_LEVEL
     , mLogLevel(static_cast<otLogLevel>(OPENTHREAD_CONFIG_INITIAL_LOG_LEVEL))
 #endif
diff --git a/src/core/common/instance.hpp b/src/core/common/instance.hpp
index 2e8df8da8..5fb20ae1d 100644
--- a/src/core/common/instance.hpp
+++ b/src/core/common/instance.hpp
@@ -298,31 +298,41 @@ private:
     Instance(void);
     void AfterInit(void);
 
+    // Order of variables (their initialization in `Instance`)
+    // is important.
+    //
+    // Tasklet and Timer Schedulers are first to ensure other
+    // objects/classes can use them from their constructors.
+
+    TaskletScheduler    mTaskletScheduler;
     TimerMilliScheduler mTimerMilliScheduler;
 #if OPENTHREAD_CONFIG_ENABLE_PLATFORM_USEC_TIMER
     TimerMicroScheduler mTimerMicroScheduler;
 #endif
-    TaskletScheduler mTaskletScheduler;
 
 #if OPENTHREAD_MTD || OPENTHREAD_FTD
-    otHandleActiveScanResult mActiveScanCallback;
-    void *                   mActiveScanCallbackContext;
-    otHandleEnergyScanResult mEnergyScanCallback;
-    void *                   mEnergyScanCallbackContext;
-
-    Notifier mNotifier;
-    Settings mSettings;
-
+    // RandomManager is initialized before other objects. Note that it
+    // requires MbedTls which itself may use Heap.
+#if !OPENTHREAD_ENABLE_MULTIPLE_INSTANCES
+    Utils::Heap mHeap;
+#endif
     Crypto::MbedTls mMbedTls;
 #endif // OPENTHREAD_MTD || OPENTHREAD_FTD
 
     RandomManager mRandomManager;
 
 #if OPENTHREAD_MTD || OPENTHREAD_FTD
+    // Notifier, Settings, and MessagePool are initialized  before
+    // other member variables since other classes/objects from their
+    // constructor may use them.
+    Notifier    mNotifier;
+    Settings    mSettings;
+    MessagePool mMessagePool;
 
-#if !OPENTHREAD_ENABLE_MULTIPLE_INSTANCES
-    Utils::Heap mHeap;
-#endif
+    otHandleActiveScanResult mActiveScanCallback;
+    void *                   mActiveScanCallbackContext;
+    otHandleEnergyScanResult mEnergyScanCallback;
+    void *                   mEnergyScanCallbackContext;
 
     Ip6::Ip6    mIp6;
     ThreadNetif mThreadNetif;
@@ -347,7 +357,6 @@ private:
     AnnounceSender mAnnounceSender;
 #endif
 
-    MessagePool mMessagePool;
 #endif // OPENTHREAD_MTD || OPENTHREAD_FTD
 #if OPENTHREAD_RADIO || OPENTHREAD_ENABLE_RAW_LINK_API
     Mac::LinkRaw mLinkRaw;