diff --git a/modules/bitgo/test/v2/unit/wallet.ts b/modules/bitgo/test/v2/unit/wallet.ts
index 68568aef7b..59b9508efe 100644
--- a/modules/bitgo/test/v2/unit/wallet.ts
+++ b/modules/bitgo/test/v2/unit/wallet.ts
@@ -4420,6 +4420,27 @@ describe('V2 Wallet:', function () {
           txRequest.should.deepEqual(txRequestForMessageSigning);
         });
 
+        it('should include preparedTransaction in the msgrequests body when provided', async function () {
+          const preparedTransaction = 'base64-prepared-transaction-bytes';
+          let capturedBody: any;
+          nock(bgUrl)
+            .post(`/api/v2/wallet/${tssEthWallet.id()}/msgrequests`, (body) => {
+              capturedBody = body;
+              return true;
+            })
+            .reply(200, txRequestForMessageSigning);
+
+          await tssEthWallet.buildSignMessageRequest({
+            message: {
+              messageRaw,
+              messageStandardType: MessageStandardType.EIP191,
+              preparedTransaction,
+            },
+          });
+
+          capturedBody.intent.preparedTransaction.should.equal(preparedTransaction);
+        });
+
         it(`[${coinName}] should sign message`, async function () {
           const signMessageTssSpy = sinon.spy(tssEthWallet, 'signMessageTss' as any);
           nock(bgUrl)
@@ -4475,6 +4496,25 @@ describe('V2 Wallet:', function () {
           );
         });
 
+        it(`[${coinName}] should include preparedTransaction when signing a fresh message request`, async function () {
+          const preparedTransaction = 'base64-prepared-transaction-bytes';
+          let capturedBody: any;
+          nock(bgUrl)
+            .post(`/api/v2/wallet/${tssEthWallet.id()}/msgrequests`, (body) => {
+              capturedBody = body;
+              return true;
+            })
+            .reply(200, txRequestForMessageSigning);
+
+          await tssEthWallet.signMessage({
+            reqId,
+            message: { messageRaw, messageStandardType: MessageStandardType.EIP191, preparedTransaction },
+            prv: 'secretKey',
+          });
+
+          capturedBody.intent.preparedTransaction.should.equal(preparedTransaction);
+        });
+
         it('should fail to sign message with empty prv', async function () {
           await tssEthWallet
             .signMessage({
diff --git a/modules/sdk-core/src/bitgo/baseCoin/iBaseCoin.ts b/modules/sdk-core/src/bitgo/baseCoin/iBaseCoin.ts
index 4a825f389c..8460690fbb 100644
--- a/modules/sdk-core/src/bitgo/baseCoin/iBaseCoin.ts
+++ b/modules/sdk-core/src/bitgo/baseCoin/iBaseCoin.ts
@@ -457,6 +457,8 @@ export interface Message extends BaseSignable {
   messageEncoded?: string;
   messageStandardType?: MessageStandardType;
   signerAddress?: string;
+  /** Base64-encoded prepared transaction bytes required by Canton message signing. */
+  preparedTransaction?: string;
 }
 
 export interface MessageTypeProperty {
diff --git a/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts b/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts
index 7877136bfc..311527e192 100644
--- a/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts
+++ b/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts
@@ -473,6 +473,7 @@ export default class BaseTssUtils<KeyShare> extends MpcUtils implements ITssUtil
       messageStandardType: params.messageStandardType ?? MessageStandardType.UNKNOWN,
       messageEncoded: params.messageEncoded ?? '',
       signerAddress: params.signerAddress,
+      preparedTransaction: params.preparedTransaction,
     };
 
     return this.buildSignMessageRequestBase(intent, apiVersion, params.reqId);
diff --git a/modules/sdk-core/src/bitgo/utils/tss/baseTypes.ts b/modules/sdk-core/src/bitgo/utils/tss/baseTypes.ts
index 5ad412fd8b..a1f05d48fe 100644
--- a/modules/sdk-core/src/bitgo/utils/tss/baseTypes.ts
+++ b/modules/sdk-core/src/bitgo/utils/tss/baseTypes.ts
@@ -304,6 +304,8 @@ export interface IntentOptionsForMessage extends IntentOptionsBase {
   messageEncoded?: string;
   messageStandardType?: MessageStandardType;
   signerAddress?: string;
+  /** Base64-encoded prepared transaction bytes required by Canton message signing. */
+  preparedTransaction?: string;
 }
 
 export interface IntentOptionsForTypedData extends IntentOptionsBase {
@@ -417,6 +419,8 @@ export interface PopulatedIntentForMessageSigning extends PopulatedIntentBase {
   custodianMessageId?: string;
   messageStandardType?: MessageStandardType;
   signerAddress?: string;
+  /** Base64-encoded prepared transaction bytes required by Canton message signing. */
+  preparedTransaction?: string;
 }
 
 export interface PopulatedIntentForTypedDataSigning extends PopulatedIntentBase {
diff --git a/modules/sdk-core/src/bitgo/wallet/wallet.ts b/modules/sdk-core/src/bitgo/wallet/wallet.ts
index 0cc72ea097..9cff4fa808 100644
--- a/modules/sdk-core/src/bitgo/wallet/wallet.ts
+++ b/modules/sdk-core/src/bitgo/wallet/wallet.ts
@@ -2527,6 +2527,7 @@ export class Wallet implements IWallet {
         messageRaw,
         messageStandardType,
         signerAddress: params.message.signerAddress,
+        preparedTransaction: params.message.preparedTransaction,
       };
 
       if (!this.tssUtils) {
@@ -5143,6 +5144,7 @@ export class Wallet implements IWallet {
           messageRaw,
           messageStandardType: params.message.messageStandardType,
           signerAddress: params.message.signerAddress,
+          preparedTransaction: params.message.preparedTransaction,
         };
         txRequest = await this.tssUtils!.buildSignMessageRequest(intentOption);
         params.message.txRequestId = txRequest.txRequestId;