diff --git a/lib/shared/avatar-utils.js b/lib/shared/avatar-utils.js
new file mode 100644
--- /dev/null
+++ b/lib/shared/avatar-utils.js
@@ -0,0 +1,46 @@
+// @flow
+
+import stringHash from 'string-hash';
+
+import { selectedThreadColors } from './thread-utils.js';
+import type { EmojiAvatar } from '../types/avatar-types.js';
+
+const defaultEmojiAvatars: $ReadOnlyArray<EmojiAvatar> = [
+  { color: selectedThreadColors[7], emoji: '😀' },
+  { color: selectedThreadColors[0], emoji: '😆' },
+  { color: selectedThreadColors[1], emoji: '🤩' },
+  { color: selectedThreadColors[7], emoji: '🏈' },
+  { color: selectedThreadColors[2], emoji: '👻' },
+  { color: selectedThreadColors[3], emoji: '🧑‍🚀' },
+  { color: selectedThreadColors[4], emoji: '🎩' },
+  { color: selectedThreadColors[5], emoji: '🍦' },
+  { color: selectedThreadColors[6], emoji: '🚀' },
+  { color: selectedThreadColors[8], emoji: '🥰' },
+  { color: selectedThreadColors[3], emoji: '🐬' },
+  { color: selectedThreadColors[4], emoji: '🍀' },
+  { color: selectedThreadColors[9], emoji: '🍕' },
+  { color: selectedThreadColors[0], emoji: '🙄' },
+  { color: selectedThreadColors[1], emoji: '🥳' },
+  { color: selectedThreadColors[7], emoji: '🥸' },
+  { color: selectedThreadColors[2], emoji: '🦋' },
+  { color: selectedThreadColors[9], emoji: '🏆' },
+  { color: selectedThreadColors[5], emoji: '🎲' },
+  { color: selectedThreadColors[8], emoji: '🏀' },
+];
+
+function getAvatarForUser(
+  user: ?{ +avatar?: ?EmojiAvatar, +username?: ?string, ... },
+): EmojiAvatar {
+  if (user?.avatar) {
+    return user.avatar;
+  }
+
+  if (!user?.username) {
+    return defaultEmojiAvatars[0];
+  }
+
+  const avatarIndex = stringHash(user.username) % defaultEmojiAvatars.length;
+  return defaultEmojiAvatars[avatarIndex];
+}
+
+export { getAvatarForUser };
diff --git a/lib/types/avatar-types.js b/lib/types/avatar-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/avatar-types.js
@@ -0,0 +1,6 @@
+// @flow
+
+export type EmojiAvatar = {
+  +emoji: string,
+  +color: string,
+};