diff --git a/ts/test/types/Conversation_test.ts b/ts/test/types/Conversation_test.ts
new file mode 100644
index 0000000000..f5aea6fc6a
--- /dev/null
+++ b/ts/test/types/Conversation_test.ts
@@ -0,0 +1,102 @@
+import 'mocha';
+import { assert } from 'chai';
+
+import * as Conversation from '../../types/Conversation';
+import {
+  IncomingMessage,
+  OutgoingMessage,
+  VerifiedChangeMessage,
+} from '../../types/Message';
+
+describe('Conversation', () => {
+  describe('createLastMessageUpdate', () => {
+    it('should reset last message if conversation has no messages', () => {
+      const input = {
+        currentLastMessageText: null,
+        currentTimestamp: null,
+        lastMessage: null,
+        lastMessageNotificationText: null,
+      };
+      const expected = {
+        lastMessage: '',
+        timestamp: null,
+      };
+
+      const actual = Conversation.createLastMessageUpdate(input);
+      assert.deepEqual(actual, expected);
+    });
+
+    context('for regular message', () => {
+      it('should update last message text and timestamp', () => {
+        const input = {
+          currentLastMessageText: 'Existing message',
+          currentTimestamp: 555,
+          lastMessage: {
+             type: 'outgoing',
+             conversationId: 'foo',
+             sent_at: 666,
+             timestamp: 666,
+          } as OutgoingMessage,
+          lastMessageNotificationText: 'New outgoing message',
+        };
+        const expected = {
+          lastMessage: 'New outgoing message',
+          timestamp: 666,
+        };
+
+        const actual = Conversation.createLastMessageUpdate(input);
+        assert.deepEqual(actual, expected);
+      });
+    });
+    context('for verified change message', () => {
+      it('should skip update', () => {
+        const input = {
+          currentLastMessageText: 'bingo',
+          currentTimestamp: 555,
+          lastMessage: {
+             type: 'verified-change',
+             conversationId: 'foo',
+             sent_at: 666,
+             timestamp: 666,
+          } as VerifiedChangeMessage,
+          lastMessageNotificationText: 'Verified Changed',
+        };
+        const expected = {
+          lastMessage: 'bingo',
+          timestamp: 555,
+        };
+
+        const actual = Conversation.createLastMessageUpdate(input);
+        assert.deepEqual(actual, expected);
+      });
+    });
+
+    context('for expired message', () => {
+      it('should update message but not timestamp (to prevent bump to top)', () => {
+        const input = {
+          currentLastMessageText: 'I am expired',
+          currentTimestamp: 555,
+          lastMessage: {
+             type: 'incoming',
+             conversationId: 'foo',
+             sent_at: 666,
+             timestamp: 666,
+             expirationTimerUpdate: {
+               expireTimer: 111,
+               fromSync: false,
+               source: '+12223334455',
+             },
+          } as IncomingMessage,
+          lastMessageNotificationText: 'Last message before expired',
+        };
+        const expected = {
+          lastMessage: 'Last message before expired',
+          timestamp: 555,
+        };
+
+        const actual = Conversation.createLastMessageUpdate(input);
+        assert.deepEqual(actual, expected);
+      });
+    });
+  });
+});
diff --git a/ts/types/Conversation.ts b/ts/types/Conversation.ts
new file mode 100644
index 0000000000..e31b3b0a60
--- /dev/null
+++ b/ts/types/Conversation.ts
@@ -0,0 +1,45 @@
+import is from '@sindresorhus/is';
+import { Message } from './Message';
+
+
+interface ConversationLastMessageUpdate {
+  lastMessage: string | null;
+  timestamp: number | null;
+}
+
+export const createLastMessageUpdate = ({
+  currentLastMessageText,
+  currentTimestamp,
+  lastMessage,
+  lastMessageNotificationText,
+}: {
+  currentLastMessageText: string | null,
+  currentTimestamp: number | null,
+  lastMessage: Message | null,
+  lastMessageNotificationText: string | null,
+}): ConversationLastMessageUpdate => {
+  if (lastMessage === null) {
+    return {
+      lastMessage: '',
+      timestamp: null,
+    };
+  }
+
+  const { type } = lastMessage;
+  const isVerifiedChangeMessage = type === 'verified-change';
+  const isExpiringMessage = is.object(lastMessage.expirationTimerUpdate);
+  const shouldUpdateTimestamp = !isVerifiedChangeMessage && !isExpiringMessage;
+
+  const newTimestamp = shouldUpdateTimestamp ?
+    lastMessage.sent_at :
+    currentTimestamp;
+
+  const shouldUpdateLastMessageText = !isVerifiedChangeMessage;
+  const newLastMessageText = shouldUpdateLastMessageText ?
+    lastMessageNotificationText : currentLastMessageText;
+
+  return {
+    lastMessage: newLastMessageText,
+    timestamp: newTimestamp,
+  };
+};