diff --git a/src/lib/testFlags.ts b/src/lib/testFlags.ts
index 19198fb8e8..a789a50884 100644
--- a/src/lib/testFlags.ts
+++ b/src/lib/testFlags.ts
@@ -68,6 +68,10 @@ class TestFlags {
     return this.booleanFlag(this.queryParams.enable_turnkey);
   }
 
+  get enablePasskeyAuth() {
+    return this.booleanFlag(this.queryParams.passkey_auth);
+  }
+
   get spot() {
     return this.booleanFlag(this.queryParams.spot);
   }
diff --git a/src/providers/TurnkeyAuthProvider.tsx b/src/providers/TurnkeyAuthProvider.tsx
index a8086507b5..8174da4d16 100644
--- a/src/providers/TurnkeyAuthProvider.tsx
+++ b/src/providers/TurnkeyAuthProvider.tsx
@@ -3,7 +3,7 @@ import { createContext, useCallback, useContext, useEffect, useMemo, useState }
 import { logBonsaiError, logBonsaiInfo } from '@/bonsai/logs';
 import { selectIndexerUrl } from '@/bonsai/socketSelectors';
 import { useMutation } from '@tanstack/react-query';
-import { TurnkeyIndexedDbClient } from '@turnkey/sdk-browser';
+import { SessionType, TurnkeyIndexedDbClient } from '@turnkey/sdk-browser';
 import { useTurnkey } from '@turnkey/sdk-react';
 import { jwtDecode } from 'jwt-decode';
 import { useSearchParams } from 'react-router-dom';
@@ -69,7 +69,7 @@ const useTurnkeyAuthContext = () => {
   const stringGetter = useStringGetter();
   const indexerUrl = useAppSelector(selectIndexerUrl);
   const sourceAccount = useAppSelector(getSourceAccount);
-  const { indexedDbClient, authIframeClient } = useTurnkey();
+  const { indexedDbClient, authIframeClient, passkeyClient } = useTurnkey();
   const { dydxAddress: connectedDydxAddress, setWalletFromSignature, selectWallet } = useAccounts();
   const [searchParams, setSearchParams] = useSearchParams();
   const [emailToken, setEmailToken] = useState<string>();
@@ -85,6 +85,7 @@ const useTurnkeyAuthContext = () => {
     onboardDydx,
     targetPublicKeys,
     getUploadAddressPayload,
+    fetchCredentialId,
   } = useTurnkeyWallet();
 
   /* ----------------------------- Upload Address ----------------------------- */
@@ -217,7 +218,9 @@ const useTurnkeyAuthContext = () => {
           handleEmailResponse({ userEmail, response });
           setEmailSignInStatus('idle');
           break;
-        case LoginMethod.Passkey: // TODO: handle passkey response
+        case LoginMethod.Passkey:
+          handlePasskeyResponse({ response });
+          break;
         default:
           throw new Error('Current unsupported login method');
       }
@@ -332,6 +335,49 @@ const useTurnkeyAuthContext = () => {
     [onboardDydx, indexedDbClient, setWalletFromSignature, uploadAddress]
   );
 
+  const handlePasskeyResponse = useCallback(
+    async ({ response }: { response: TurnkeyOAuthResponse }) => {
+      const { salt, dydxAddress: uploadedDydxAddress } = response as {
+        salt?: string;
+        dydxAddress?: string;
+      };
+
+      if (!passkeyClient) {
+        throw new Error('Passkey client is not available');
+      }
+      const derivedDydxAddress = await onboardDydx({
+        salt,
+        setWalletFromSignature,
+        tkClient: indexedDbClient,
+      });
+
+      if (uploadedDydxAddress === '' && derivedDydxAddress) {
+        try {
+          await uploadAddress({ tkClient: indexedDbClient, dydxAddress: derivedDydxAddress });
+        } catch (uploadAddressError) {
+          if (
+            uploadAddressError instanceof Error &&
+            !uploadAddressError.message.includes('Dydx address already uploaded')
+          ) {
+            throw uploadAddressError;
+          }
+        }
+      }
+
+      setEmailSignInStatus('success');
+      setEmailSignInError(undefined);
+    },
+    [
+      onboardDydx,
+      indexedDbClient,
+      setWalletFromSignature,
+      uploadAddress,
+      setEmailSignInStatus,
+      setEmailSignInError,
+      passkeyClient,
+    ]
+  );
+
   /* ----------------------------- Email Sign In ----------------------------- */
 
   const handleEmailResponse = useCallback(
@@ -524,6 +570,49 @@ const useTurnkeyAuthContext = () => {
     setEmailSignInError(undefined);
   }, [searchParams, setSearchParams]);
 
+  /* ----------------------------- Passkey Sign In ----------------------------- */
+
+  const signInWithPasskey = useCallback(async () => {
+    try {
+      if (!passkeyClient) {
+        throw new Error('Passkey client is not available');
+      }
+
+      await indexedDbClient!.resetKeyPair();
+      const pubKey = await indexedDbClient!.getPublicKey();
+      if (!pubKey) {
+        throw new Error('No public key available for passkey session');
+      }
+      // Authenticate with the user's passkey for the returned sub-organization
+      await passkeyClient.loginWithPasskey({
+        sessionType: SessionType.READ_WRITE,
+        publicKey: pubKey,
+        expirationSeconds: (60 * 15).toString(), // 15 minutes
+      });
+
+      const credentialId = await fetchCredentialId(indexedDbClient);
+      if (!credentialId) {
+        throw new Error('No user found');
+      }
+
+      // dummy body used to get salt.
+      const bodyWithAttestation: SignInBody = {
+        signinMethod: 'passkey',
+        challenge: credentialId,
+        attestation: {
+          credentialId,
+        },
+      };
+
+      sendSignInRequest({
+        body: JSON.stringify(bodyWithAttestation),
+        loginMethod: LoginMethod.Passkey,
+      });
+    } catch (error) {
+      logBonsaiError('TurnkeyOnboarding', 'Error signing in with passkey', { error });
+    }
+  }, [passkeyClient, indexedDbClient, fetchCredentialId, sendSignInRequest]);
+
   /* ----------------------------- Side Effects ----------------------------- */
 
   /**
@@ -592,6 +681,7 @@ const useTurnkeyAuthContext = () => {
     isUploadingAddress,
     signInWithOauth,
     signInWithOtp,
+    signInWithPasskey,
     resetEmailSignInStatus,
   };
 };
diff --git a/src/providers/TurnkeyWalletProvider.tsx b/src/providers/TurnkeyWalletProvider.tsx
index 45e2668f49..240ba0511b 100644
--- a/src/providers/TurnkeyWalletProvider.tsx
+++ b/src/providers/TurnkeyWalletProvider.tsx
@@ -123,6 +123,33 @@ const useTurnkeyWalletContext = () => {
   }, [authIframeClient]);
 
   /* ----------------------------- Onboarding Functions ----------------------------- */
+
+  // used to fetch the credential id for the passkey sign in
+  const fetchCredentialId = useCallback(
+    async (tkClient?: TurnkeyIndexedDbClient): Promise<string | undefined> => {
+      if (turnkey == null || tkClient == null) {
+        return undefined;
+      }
+      // Try and get the current user
+      const token = await turnkey.getSession();
+
+      // If the user is not found, we assume the user is not logged in
+      if (!token?.expiry || token.expiry > Date.now()) {
+        return undefined;
+      }
+
+      const { user: indexedDbUser } = await tkClient.getUser({
+        organizationId: token.organizationId,
+        userId: token.userId,
+      });
+      if (indexedDbUser.authenticators.length === 0) {
+        return undefined;
+      }
+      return indexedDbUser.authenticators[0]?.credentialId;
+    },
+    [turnkey]
+  );
+
   const fetchUser = useCallback(
     async (tkClient?: TurnkeyIndexedDbClient): Promise<UserSession | undefined> => {
       const isIndexedDbFlow = tkClient instanceof TurnkeyIndexedDbClient;
@@ -202,7 +229,6 @@ const useTurnkeyWalletContext = () => {
       tkClient?: TurnkeyIndexedDbClient;
     }) => {
       const selectedTurnkeyWallet = primaryTurnkeyWallet ?? (await getPrimaryUserWallets(tkClient));
-
       const ethAccount = selectedTurnkeyWallet?.accounts.find(
         (account) => account.addressFormat === AddressFormat.Ethereum
       );
@@ -341,6 +367,7 @@ const useTurnkeyWalletContext = () => {
     isNewTurnkeyUser,
 
     endTurnkeySession,
+    fetchCredentialId,
     onboardDydx,
     getUploadAddressPayload,
     setIsNewTurnkeyUser,
diff --git a/src/types/turnkey.ts b/src/types/turnkey.ts
index 2539e6d37f..0b50f120a0 100644
--- a/src/types/turnkey.ts
+++ b/src/types/turnkey.ts
@@ -49,7 +49,7 @@ export type GoogleIdTokenPayload = {
 
 export type SignInBody =
   | {
-      signinMethod: 'social' | 'passkey';
+      signinMethod: 'social';
       targetPublicKey: string;
       provider: 'google' | 'apple';
       oidcToken: string;
@@ -57,9 +57,27 @@ export type SignInBody =
     }
   | {
       signinMethod: 'email';
-      targetPublicKey: string;
+      targetPublicKey?: string;
       userEmail: string;
       magicLink: string;
+    }
+  | {
+      signinMethod: 'passkey';
+      // In a full implementation these are required; left optional to allow
+      // initiating the flow and handling multi-step server responses.
+      challenge?: string;
+      attestation?: {
+        transports?: Array<
+          | 'AUTHENTICATOR_TRANSPORT_BLE'
+          | 'AUTHENTICATOR_TRANSPORT_INTERNAL'
+          | 'AUTHENTICATOR_TRANSPORT_NFC'
+          | 'AUTHENTICATOR_TRANSPORT_USB'
+          | 'AUTHENTICATOR_TRANSPORT_HYBRID'
+        >;
+        attestationObject?: string; // base64url
+        clientDataJson?: string; // base64url
+        credentialId: string; // base64url
+      };
     };
 
 export type TurnkeyEmailOnboardingData = {
diff --git a/src/views/dialogs/OnboardingDialog/SignIn.tsx b/src/views/dialogs/OnboardingDialog/SignIn.tsx
index 721defc6f9..19fb163602 100644
--- a/src/views/dialogs/OnboardingDialog/SignIn.tsx
+++ b/src/views/dialogs/OnboardingDialog/SignIn.tsx
@@ -51,7 +51,7 @@ export const SignIn = ({
   const [email, setEmail] = useState('');
   const [isLoading, setIsLoading] = useState(false);
   const { authIframeClient } = useTurnkey();
-  const { signInWithOtp } = useTurnkeyAuth();
+  const { signInWithOtp, signInWithPasskey } = useTurnkeyAuth();
   const appTheme = useAppSelector(getAppTheme);
   const { tos, privacy } = useURLConfigs();
   const displayedWallets = useDisplayedWallets();
@@ -137,19 +137,21 @@ export const SignIn = ({
           <$HorizontalSeparatorFiller $isLightMode={appTheme === AppTheme.Light} />
         </div>
 
-        {/* <$OtherOptionButton
-          type={ButtonType.Button}
-          action={ButtonAction.Base}
-          size={ButtonSize.BasePlus}
-          onClick={onSignInWithPasskey}
-        >
-          <div tw="row gap-0.5">
-            <Icon iconName={IconName.Passkey} />
-            {stringGetter({ key: STRING_KEYS.SIGN_IN_PASSKEY })}
-          </div>
+        {testFlags.enablePasskeyAuth && (
+          <$OtherOptionButton
+            type={ButtonType.Button}
+            action={ButtonAction.Base}
+            size={ButtonSize.BasePlus}
+            onClick={signInWithPasskey}
+          >
+            <div tw="row gap-0.5">
+              <Icon iconName={IconName.Passkey} />
+              {stringGetter({ key: STRING_KEYS.SIGN_IN_PASSKEY })}
+            </div>
 
-          <Icon tw="text-color-layer-7" iconName={IconName.ChevronRight} />
-        </$OtherOptionButton> */}
+            <Icon tw="text-color-layer-7" iconName={IconName.ChevronRight} />
+          </$OtherOptionButton>
+        )}
 
         {displayedWallets
           .filter(