diff --git a/quic/core/http/end_to_end_test.cc b/quic/core/http/end_to_end_test.cc
index 399e19f..6b7bfd5 100644
--- a/quic/core/http/end_to_end_test.cc
+++ b/quic/core/http/end_to_end_test.cc
@@ -70,6 +70,9 @@
 using spdy::SpdyHeaderBlock;
 using spdy::SpdySerializedFrame;
 using spdy::SpdySettingsIR;
+using ::testing::_;
+using ::testing::Invoke;
+using ::testing::NiceMock;
 
 namespace quic {
 namespace test {
@@ -662,9 +665,9 @@
 TEST_P(EndToEndTest, SimpleRequestResponseForcedVersionNegotiation) {
   client_supported_versions_.insert(client_supported_versions_.begin(),
                                     QuicVersionReservedForNegotiation());
-  testing::NiceMock<MockQuicConnectionDebugVisitor> visitor;
+  NiceMock<MockQuicConnectionDebugVisitor> visitor;
   connection_debug_visitor_ = &visitor;
-  EXPECT_CALL(visitor, OnVersionNegotiationPacket(testing::_)).Times(1);
+  EXPECT_CALL(visitor, OnVersionNegotiationPacket(_)).Times(1);
   ASSERT_TRUE(Initialize());
   ASSERT_TRUE(ServerSendsVersionNegotiation());
 
@@ -2542,7 +2545,7 @@
   QuicFramer framer(server_supported_versions_, QuicTime::Zero(),
                     Perspective::IS_SERVER, kQuicDefaultConnectionIdLength);
   std::unique_ptr<QuicEncryptedPacket> packet;
-  testing::NiceMock<MockQuicConnectionDebugVisitor> visitor;
+  NiceMock<MockQuicConnectionDebugVisitor> visitor;
   GetClientConnection()->set_debug_visitor(&visitor);
   if (VersionHasIetfInvariantHeader(client_connection->transport_version())) {
     packet = framer.BuildIetfStatelessResetPacket(incorrect_connection_id,
@@ -2618,7 +2621,7 @@
           VersionHasIetfInvariantHeader(client_connection->transport_version()),
           client_connection->version().HasLengthPrefixedConnectionIds(),
           server_supported_versions_));
-  testing::NiceMock<MockQuicConnectionDebugVisitor> visitor;
+  NiceMock<MockQuicConnectionDebugVisitor> visitor;
   client_connection->set_debug_visitor(&visitor);
   EXPECT_CALL(visitor, OnIncorrectConnectionId(incorrect_connection_id))
       .Times(1);
@@ -4264,6 +4267,42 @@
                   ->CanCreatePushStreamWithId(kMaxQuicStreamId));
 }
 
+TEST_P(EndToEndTest, CustomTransportParameters) {
+  if (!version_.UsesTls()) {
+    // Custom transport parameters are only supported with TLS.
+    ASSERT_TRUE(Initialize());
+    return;
+  }
+  constexpr auto kCustomParameter =
+      static_cast<TransportParameters::TransportParameterId>(0xff34);
+  client_config_.custom_transport_parameters_to_send()[kCustomParameter] =
+      "test";
+  NiceMock<MockQuicConnectionDebugVisitor> visitor;
+  connection_debug_visitor_ = &visitor;
+  EXPECT_CALL(visitor, OnTransportParametersSent(_))
+      .WillOnce(Invoke([kCustomParameter](
+                           const TransportParameters& transport_parameters) {
+        ASSERT_NE(transport_parameters.custom_parameters.find(kCustomParameter),
+                  transport_parameters.custom_parameters.end());
+        EXPECT_EQ(transport_parameters.custom_parameters.at(kCustomParameter),
+                  "test");
+      }));
+  EXPECT_CALL(visitor, OnTransportParametersReceived(_)).Times(1);
+  ASSERT_TRUE(Initialize());
+
+  EXPECT_TRUE(client_->client()->WaitForCryptoHandshakeConfirmed());
+
+  server_thread_->Pause();
+  QuicConfig server_config = *GetServerSession()->config();
+  server_thread_->Resume();
+  ASSERT_NE(server_config.received_custom_transport_parameters().find(
+                kCustomParameter),
+            server_config.received_custom_transport_parameters().end());
+  EXPECT_EQ(
+      server_config.received_custom_transport_parameters().at(kCustomParameter),
+      "test");
+}
+
 TEST_P(EndToEndTest, DISABLED_CustomTransportParameters) {
   // TODO(b/155316241): Enable this test.
   constexpr auto kCustomParameter =
diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index 0747d4f..bb32b6e 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -841,6 +841,20 @@
   }
 }
 
+void QuicConnection::OnTransportParametersSent(
+    const TransportParameters& transport_parameters) const {
+  if (debug_visitor_ != nullptr) {
+    debug_visitor_->OnTransportParametersSent(transport_parameters);
+  }
+}
+
+void QuicConnection::OnTransportParametersReceived(
+    const TransportParameters& transport_parameters) const {
+  if (debug_visitor_ != nullptr) {
+    debug_visitor_->OnTransportParametersReceived(transport_parameters);
+  }
+}
+
 void QuicConnection::OnDecryptedPacket(EncryptionLevel level) {
   last_decrypted_packet_level_ = level;
   last_packet_decrypted_ = true;
diff --git a/quic/core/quic_connection.h b/quic/core/quic_connection.h
index 6586fb2..9e39777 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -26,6 +26,7 @@
 
 #include "net/third_party/quiche/src/quic/core/crypto/quic_decrypter.h"
 #include "net/third_party/quiche/src/quic/core/crypto/quic_encrypter.h"
+#include "net/third_party/quiche/src/quic/core/crypto/transport_parameters.h"
 #include "net/third_party/quiche/src/quic/core/frames/quic_max_streams_frame.h"
 #include "net/third_party/quiche/src/quic/core/proto/cached_network_parameters_proto.h"
 #include "net/third_party/quiche/src/quic/core/quic_alarm.h"
@@ -341,6 +342,14 @@
 
   // Called when |count| packet numbers have been skipped.
   virtual void OnNPacketNumbersSkipped(QuicPacketCount /*count*/) {}
+
+  // Called for QUIC+TLS versions when we send transport parameters.
+  virtual void OnTransportParametersSent(
+      const TransportParameters& /*transport_parameters*/) {}
+
+  // Called for QUIC+TLS versions when we receive transport parameters.
+  virtual void OnTransportParametersReceived(
+      const TransportParameters& /*transport_parameters*/) {}
 };
 
 class QUIC_EXPORT_PRIVATE QuicConnectionHelperInterface {
@@ -965,6 +974,14 @@
   // Called when version is considered negotiated.
   void OnSuccessfulVersionNegotiation();
 
+  // Called for QUIC+TLS versions when we send transport parameters.
+  void OnTransportParametersSent(
+      const TransportParameters& transport_parameters) const;
+
+  // Called for QUIC+TLS versions when we receive transport parameters.
+  void OnTransportParametersReceived(
+      const TransportParameters& transport_parameters) const;
+
  protected:
   // Calls cancel() on all the alarms owned by this connection.
   void CancelAllAlarms();
diff --git a/quic/core/tls_client_handshaker.cc b/quic/core/tls_client_handshaker.cc
index 30a9ac4..aed628e 100644
--- a/quic/core/tls_client_handshaker.cc
+++ b/quic/core/tls_client_handshaker.cc
@@ -216,6 +216,9 @@
     params.google_quic_params->SetStringPiece(kUAID, user_agent_id_);
   }
 
+  // Notify QuicConnectionDebugVisitor.
+  session()->connection()->OnTransportParametersSent(params);
+
   std::vector<uint8_t> param_bytes;
   return SerializeTransportParameters(session()->connection()->version(),
                                       params, &param_bytes) &&
@@ -244,6 +247,10 @@
     return false;
   }
 
+  // Notify QuicConnectionDebugVisitor.
+  session()->connection()->OnTransportParametersReceived(
+      *received_transport_params_);
+
   // When interoperating with non-Google implementations that do not send
   // the version extension, set it to what we expect.
   if (received_transport_params_->version == 0) {
diff --git a/quic/core/tls_server_handshaker.cc b/quic/core/tls_server_handshaker.cc
index 5bd5b3d..99333a6 100644
--- a/quic/core/tls_server_handshaker.cc
+++ b/quic/core/tls_server_handshaker.cc
@@ -284,6 +284,9 @@
     return false;
   }
 
+  // Notify QuicConnectionDebugVisitor.
+  session()->connection()->OnTransportParametersReceived(client_params);
+
   // When interoperating with non-Google implementations that do not send
   // the version extension, set it to what we expect.
   if (client_params.version == 0) {
@@ -318,6 +321,10 @@
 
   // TODO(nharper): Provide an actual value for the stateless reset token.
   server_params.stateless_reset_token.resize(16);
+
+  // Notify QuicConnectionDebugVisitor.
+  session()->connection()->OnTransportParametersSent(server_params);
+
   std::vector<uint8_t> server_params_bytes;
   if (!SerializeTransportParameters(session()->connection()->version(),
                                     server_params, &server_params_bytes) ||
diff --git a/quic/test_tools/quic_test_utils.h b/quic/test_tools/quic_test_utils.h
index 7d1d9db..031833d 100644
--- a/quic/test_tools/quic_test_utils.h
+++ b/quic/test_tools/quic_test_utils.h
@@ -15,6 +15,7 @@
 
 #include "net/third_party/quiche/src/quic/core/congestion_control/loss_detection_interface.h"
 #include "net/third_party/quiche/src/quic/core/congestion_control/send_algorithm_interface.h"
+#include "net/third_party/quiche/src/quic/core/crypto/transport_parameters.h"
 #include "net/third_party/quiche/src/quic/core/http/quic_client_push_promise_index.h"
 #include "net/third_party/quiche/src/quic/core/http/quic_server_session_base.h"
 #include "net/third_party/quiche/src/quic/core/http/quic_spdy_session.h"
@@ -1415,6 +1416,16 @@
               OnVersionNegotiationPacket,
               (const QuicVersionNegotiationPacket&),
               (override));
+
+  MOCK_METHOD(void,
+              OnTransportParametersSent,
+              (const TransportParameters&),
+              (override));
+
+  MOCK_METHOD(void,
+              OnTransportParametersReceived,
+              (const TransportParameters&),
+              (override));
 };
 
 class MockReceivedPacketManager : public QuicReceivedPacketManager {