diff --git a/lib/shared/messages/text-message-spec.js b/lib/shared/messages/text-message-spec.js
--- a/lib/shared/messages/text-message-spec.js
+++ b/lib/shared/messages/text-message-spec.js
@@ -28,7 +28,10 @@
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { ET } from '../../utils/entity-text.js';
 import { useDispatchActionPromise } from '../../utils/redux-promise-utils.js';
+import { useSelector } from '../../utils/redux-utils.js';
 import { useAddDMThreadMembers } from '../dm-ops/dm-op-utils.js';
+import { useModifyFarcasterMembershipInput } from '../farcaster/farcaster-api.js';
+import { useRefreshFarcasterConversation } from '../farcaster/farcaster-hooks.js';
 import {
   type ASTNode,
   type SingleASTNode,
@@ -294,6 +297,9 @@
     const dispatchActionPromise = useDispatchActionPromise();
     const callChangeThreadSettings = useChangeThreadSettings();
     const callAddDMThreadMembers = useAddDMThreadMembers();
+    const modifyFarcasterMembership = useModifyFarcasterMembershipInput();
+    const refreshFarcasterConversation = useRefreshFarcasterConversation();
+    const auxUserStore = useSelector(state => state.auxUserStore);
     return async (
       messageInfo: RawTextMessageInfo,
       threadInfo: ThreadInfo,
@@ -322,6 +328,9 @@
           dmAddThreadMembers: callAddDMThreadMembers,
           changeThreadSettings: callChangeThreadSettings,
           dispatchActionPromise,
+          modifyFarcasterMembership,
+          refreshFarcasterConversation,
+          auxUserStore,
         },
       );
     };
diff --git a/lib/shared/threads/protocols/farcaster-thread-protocol.js b/lib/shared/threads/protocols/farcaster-thread-protocol.js
--- a/lib/shared/threads/protocols/farcaster-thread-protocol.js
+++ b/lib/shared/threads/protocols/farcaster-thread-protocol.js
@@ -5,6 +5,7 @@
 import { fetchMessagesBeforeCursorActionTypes } from '../../../actions/message-actions.js';
 import {
   changeThreadMemberRolesActionTypes,
+  changeThreadSettingsActionTypes,
   leaveThreadActionTypes,
   removeUsersFromThreadActionTypes,
 } from '../../../actions/thread-action-types.js';
@@ -83,6 +84,8 @@
   UpdateSubscriptionUtils,
   ProtocolCreatePendingThreadInput,
   CreateRealThreadParameters,
+  ProtocolAddThreadMembersInput,
+  AddThreadMembersUtils,
   ProtocolChangeThreadMemberRolesInput,
   ChangeThreadMemberRolesUtils,
   ProtocolRemoveUsersFromThreadInput,
@@ -287,8 +290,45 @@
     throw new Error('sendReaction method is not yet implemented');
   },
 
-  addThreadMembers: async (): Promise<void> => {
-    throw new Error('addThreadMembers method is not yet implemented');
+  addThreadMembers: async (
+    input: ProtocolAddThreadMembersInput,
+    utils: AddThreadMembersUtils,
+  ): Promise<void> => {
+    const { threadInfo, newMemberIDs } = input;
+    const {
+      modifyFarcasterMembership,
+      refreshFarcasterConversation,
+      dispatchActionPromise,
+      auxUserStore,
+    } = utils;
+
+    const conversationId = conversationIDFromFarcasterThreadID(threadInfo.id);
+
+    const promise = (async () => {
+      const targetFids = newMemberIDs
+        .map(memberID => {
+          const targetFid =
+            auxUserStore.auxUserInfos[memberID]?.fid ??
+            extractFIDFromUserID(memberID);
+          return targetFid ? parseInt(targetFid, 10) : null;
+        })
+        .filter(Boolean);
+
+      if (targetFids.length > 0) {
+        const modifyFarcasterMembershipInput: ModifyFarcasterMembershipInput = {
+          conversationId,
+          action: 'add',
+          targetFids,
+        };
+
+        await modifyFarcasterMembership(modifyFarcasterMembershipInput);
+        await refreshFarcasterConversation(conversationId);
+      }
+    })();
+
+    void dispatchActionPromise(changeThreadSettingsActionTypes, promise);
+
+    await promise;
   },
 
   changeThreadMemberRoles: async (
diff --git a/lib/shared/threads/thread-spec.js b/lib/shared/threads/thread-spec.js
--- a/lib/shared/threads/thread-spec.js
+++ b/lib/shared/threads/thread-spec.js
@@ -238,6 +238,11 @@
   ) => Promise<void>,
   +changeThreadSettings: UseChangeThreadSettingsInput => Promise<ChangeThreadSettingsPayload>,
   +dispatchActionPromise: DispatchActionPromise,
+  +modifyFarcasterMembership: (
+    input: ModifyFarcasterMembershipInput,
+  ) => Promise<void>,
+  +refreshFarcasterConversation: (conversationId: string) => Promise<mixed>,
+  +auxUserStore: AuxUserStore,
 };
 
 export type ProtocolChangeThreadMemberRolesInput = {
diff --git a/native/chat/settings/add-users-modal.react.js b/native/chat/settings/add-users-modal.react.js
--- a/native/chat/settings/add-users-modal.react.js
+++ b/native/chat/settings/add-users-modal.react.js
@@ -10,6 +10,8 @@
 import { threadInfoSelector } from 'lib/selectors/thread-selectors.js';
 import { userInfoSelectorForPotentialMembers } from 'lib/selectors/user-selectors.js';
 import { useAddDMThreadMembers } from 'lib/shared/dm-ops/dm-op-utils.js';
+import { useModifyFarcasterMembershipInput } from 'lib/shared/farcaster/farcaster-api.js';
+import { useRefreshFarcasterConversation } from 'lib/shared/farcaster/farcaster-hooks.js';
 import { usePotentialMemberItems } from 'lib/shared/search-utils.js';
 import { threadActualMembers } from 'lib/shared/thread-utils.js';
 import { threadSpecs } from 'lib/shared/threads/thread-specs.js';
@@ -78,6 +80,9 @@
   const dispatchActionPromise = useDispatchActionPromise();
   const userInfoInputArrayEmpty = inputLength === 0;
   const addDMThreadMembers = useAddDMThreadMembers();
+  const modifyFarcasterMembership = useModifyFarcasterMembershipInput();
+  const refreshFarcasterConversation = useRefreshFarcasterConversation();
+  const auxUserStore = useSelector(state => state.auxUserStore);
 
   const onPressAdd = React.useCallback(async () => {
     if (userInfoInputArrayEmpty) {
@@ -91,6 +96,9 @@
           dmAddThreadMembers: addDMThreadMembers,
           changeThreadSettings: callChangeThreadSettings,
           dispatchActionPromise,
+          modifyFarcasterMembership,
+          refreshFarcasterConversation,
+          auxUserStore,
         },
       );
       close();
@@ -105,10 +113,13 @@
   }, [
     userInfoInputArrayEmpty,
     threadInfo,
-    dispatchActionPromise,
-    addDMThreadMembers,
     userInfoInputIDs,
+    addDMThreadMembers,
     callChangeThreadSettings,
+    dispatchActionPromise,
+    modifyFarcasterMembership,
+    refreshFarcasterConversation,
+    auxUserStore,
     close,
     onUnknownErrorAlertAcknowledged,
   ]);
diff --git a/web/modals/threads/members/add-members-modal.react.js b/web/modals/threads/members/add-members-modal.react.js
--- a/web/modals/threads/members/add-members-modal.react.js
+++ b/web/modals/threads/members/add-members-modal.react.js
@@ -5,6 +5,8 @@
 import { useChangeThreadSettings } from 'lib/hooks/thread-hooks.js';
 import { threadInfoSelector } from 'lib/selectors/thread-selectors.js';
 import { useAddDMThreadMembers } from 'lib/shared/dm-ops/dm-op-utils.js';
+import { useModifyFarcasterMembershipInput } from 'lib/shared/farcaster/farcaster-api.js';
+import { useRefreshFarcasterConversation } from 'lib/shared/farcaster/farcaster-hooks.js';
 import { threadSpecs } from 'lib/shared/threads/thread-specs.js';
 import { useDispatchActionPromise } from 'lib/utils/redux-promise-utils.js';
 import { useSelector } from 'lib/utils/redux-utils.js';
@@ -62,6 +64,9 @@
   const callChangeThreadSettings = useChangeThreadSettings();
   const addDMThreadMembers = useAddDMThreadMembers();
   const threadInfo = useSelector(state => threadInfoSelector(state)[threadID]);
+  const modifyFarcasterMembership = useModifyFarcasterMembershipInput();
+  const refreshFarcasterConversation = useRefreshFarcasterConversation();
+  const auxUserStore = useSelector(state => state.auxUserStore);
 
   const addUsers = React.useCallback(() => {
     const newMemberIDs = Array.from(pendingUsersToAdd.keys());
@@ -72,15 +77,21 @@
         dmAddThreadMembers: addDMThreadMembers,
         changeThreadSettings: callChangeThreadSettings,
         dispatchActionPromise,
+        modifyFarcasterMembership,
+        refreshFarcasterConversation,
+        auxUserStore,
       },
     );
     onClose();
   }, [
     addDMThreadMembers,
+    auxUserStore,
     callChangeThreadSettings,
     dispatchActionPromise,
+    modifyFarcasterMembership,
     onClose,
     pendingUsersToAdd,
+    refreshFarcasterConversation,
     threadInfo,
   ]);