diff --git a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs
index 8fc8df24e0..9f4d5d2e08 100644
--- a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs
+++ b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs
@@ -16,6 +16,7 @@ internal abstract partial class DbConnectionInternal
     {
         private static int _objectTypeCount;
         internal readonly int _objectID = Interlocked.Increment(ref _objectTypeCount);
+        private TransactionCompletedEventHandler _transactionCompletedEventHandler = null;
 
         private bool _isInStasis;
 
@@ -437,15 +438,19 @@ internal void DetachTransaction(Transaction transaction, bool isExplicitlyReleas
             // potentially a multi-threaded event, so lock the connection to make sure we don't enlist in a new
             // transaction between compare and assignment. No need to short circuit outside of lock, since failed comparisons should
             // be the exception, not the rule.
-            lock (this)
+            // locking on anything other than the transaction object would lead to a thread deadlock with sys.Transaction.TransactionCompleted event.
+            lock (transaction)
             {
                 // Detach if detach-on-end behavior, or if outer connection was closed
-                DbConnection owner = (DbConnection)Owner;
-                if (isExplicitlyReleasing || UnbindOnTransactionCompletion || null == owner)
+                DbConnection owner = Owner;
+                if (isExplicitlyReleasing || UnbindOnTransactionCompletion || owner is null)
                 {
                     Transaction currentEnlistedTransaction = _enlistedTransaction;
                     if (currentEnlistedTransaction != null && transaction.Equals(currentEnlistedTransaction))
                     {
+                        // We need to remove the transaction completed event handler to cease listening for the transaction to end.
+                        currentEnlistedTransaction.TransactionCompleted -= _transactionCompletedEventHandler;
+
                         EnlistedTransaction = null;
 
                         if (IsTxRootWaitingForTxEnd)
@@ -479,7 +484,8 @@ void TransactionCompletedEvent(object sender, TransactionEventArgs e)
 
         private void TransactionOutcomeEnlist(Transaction transaction)
         {
-            transaction.TransactionCompleted += new TransactionCompletedEventHandler(TransactionCompletedEvent);
+            _transactionCompletedEventHandler ??= new TransactionCompletedEventHandler(TransactionCompletedEvent);
+            transaction.TransactionCompleted += _transactionCompletedEventHandler;
         }
 
         internal void SetInStasis()
diff --git a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs
index 848e69aa06..3ed756eef0 100644
--- a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs
+++ b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs
@@ -159,17 +159,17 @@ public byte[] Promote()
                             ValidateActiveOnConnection(connection);
 
                             connection.ExecuteTransaction(SqlInternalConnection.TransactionRequest.Promote, null, System.Data.IsolationLevel.Unspecified, _internalTransaction, true);
-                            returnValue = _connection.PromotedDTCToken;
+                            returnValue = connection.PromotedDTCToken;
 
                             // For Global Transactions, we need to set the Transaction Id since we use a Non-MSDTC Promoter type.
-                            if (_connection.IsGlobalTransaction)
+                            if (connection.IsGlobalTransaction)
                             {
                                 if (SysTxForGlobalTransactions.SetDistributedTransactionIdentifier == null)
                                 {
                                     throw SQL.UnsupportedSysTxForGlobalTransactions();
                                 }
 
-                                if (!_connection.IsGlobalTransactionsEnabledForServer)
+                                if (!connection.IsGlobalTransactionsEnabledForServer)
                                 {
                                     throw SQL.GlobalTransactionsNotEnabled();
                                 }
diff --git a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs
index a79eb68411..06b1e04712 100644
--- a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs
+++ b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/ProviderBase/DbConnectionInternal.cs
@@ -18,11 +18,10 @@ namespace Microsoft.Data.ProviderBase
     using SysTx = System.Transactions;
 
     internal abstract class DbConnectionInternal
-    { // V1.1.3300
-
-
+    {
         private static int _objectTypeCount;
         internal readonly int _objectID = Interlocked.Increment(ref _objectTypeCount);
+        private SysTx.TransactionCompletedEventHandler _transactionCompletedEventHandler = null;
 
         internal static readonly StateChangeEventArgs StateChangeClosed = new StateChangeEventArgs(ConnectionState.Open, ConnectionState.Closed);
         internal static readonly StateChangeEventArgs StateChangeOpen = new StateChangeEventArgs(ConnectionState.Closed, ConnectionState.Open);
@@ -900,15 +899,18 @@ internal void DetachTransaction(SysTx.Transaction transaction, bool isExplicitly
             // potentially a multi-threaded event, so lock the connection to make sure we don't enlist in a new
             // transaction between compare and assignment. No need to short circuit outside of lock, since failed comparisons should
             // be the exception, not the rule.
-            lock (this)
+            // locking on anything other than the transaction object would lead to a thread deadlock with sys.Transaction.TransactionCompleted event.
+            lock (transaction)
             {
                 // Detach if detach-on-end behavior, or if outer connection was closed
-                DbConnection owner = (DbConnection)Owner;
-                if (isExplicitlyReleasing || UnbindOnTransactionCompletion || null == owner)
+                DbConnection owner = Owner;
+                if (isExplicitlyReleasing || UnbindOnTransactionCompletion || owner is null)
                 {
                     SysTx.Transaction currentEnlistedTransaction = _enlistedTransaction;
                     if (currentEnlistedTransaction != null && transaction.Equals(currentEnlistedTransaction))
                     {
+                        // We need to remove the transaction completed event handler to cease listening for the transaction to end.
+                        currentEnlistedTransaction.TransactionCompleted -= _transactionCompletedEventHandler;
 
                         EnlistedTransaction = null;
 
@@ -947,7 +949,8 @@ void TransactionCompletedEvent(object sender, SysTx.TransactionEventArgs e)
         [SecurityPermission(SecurityAction.Assert, Flags = SecurityPermissionFlag.UnmanagedCode)]
         private void TransactionOutcomeEnlist(SysTx.Transaction transaction)
         {
-            transaction.TransactionCompleted += new SysTx.TransactionCompletedEventHandler(TransactionCompletedEvent);
+            _transactionCompletedEventHandler ??= new SysTx.TransactionCompletedEventHandler(TransactionCompletedEvent);
+            transaction.TransactionCompleted += _transactionCompletedEventHandler;
         }
 
         internal void SetInStasis()
diff --git a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs
index ebc234d480..e11ec36e79 100644
--- a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs
+++ b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlDelegatedTransaction.cs
@@ -192,17 +192,17 @@ public Byte[] Promote()
                                 ValidateActiveOnConnection(connection);
 
                                 connection.ExecuteTransaction(SqlInternalConnection.TransactionRequest.Promote, null, IsolationLevel.Unspecified, _internalTransaction, true);
-                                returnValue = _connection.PromotedDTCToken;
+                                returnValue = connection.PromotedDTCToken;
 
                                 // For Global Transactions, we need to set the Transaction Id since we use a Non-MSDTC Promoter type.
-                                if (_connection.IsGlobalTransaction)
+                                if (connection.IsGlobalTransaction)
                                 {
                                     if (SysTxForGlobalTransactions.SetDistributedTransactionIdentifier == null)
                                     {
                                         throw SQL.UnsupportedSysTxForGlobalTransactions();
                                     }
 
-                                    if (!_connection.IsGlobalTransactionsEnabledForServer)
+                                    if (!connection.IsGlobalTransactionsEnabledForServer)
                                     {
                                         throw SQL.GlobalTransactionsNotEnabled();
                                     }