diff --git a/lib/shared/markdown.js b/lib/shared/markdown.js
--- a/lib/shared/markdown.js
+++ b/lib/shared/markdown.js
@@ -6,6 +6,7 @@
   markdownUserMentionRegex,
   decodeChatMentionText,
 } from './mention-utils.js';
+import { useENSNames } from '../hooks/ens-cache.js';
 import type {
   ChatMentionCandidates,
   RelativeMemberInfo,
@@ -197,15 +198,28 @@
   };
 }
 
-function createMemberMapForUserMentions(
+const useENSNamesOptions = { allAtOnce: true };
+function useMemberMapForUserMentions(
   members: $ReadOnlyArray<RelativeMemberInfo>,
 ): $ReadOnlyMap<string, string> {
   const membersMap = new Map<string, string>();
-  members.forEach(member => {
-    if (member.role && member.username) {
-      membersMap.set(member.username.toLowerCase(), member.id);
+  const resolvedMembers = useENSNames(members, useENSNamesOptions);
+
+  for (let i = 0; i < members.length; i++) {
+    const member = members[i];
+    const resolvedMember = resolvedMembers[i];
+
+    const { username: rawUsername, role } = member;
+    const { username: resolvedUsername } = resolvedMember;
+
+    if (role && rawUsername) {
+      membersMap.set(rawUsername.toLowerCase(), member.id);
     }
-  });
+
+    if (resolvedUsername && resolvedUsername !== rawUsername) {
+      membersMap.set(resolvedUsername.toLowerCase(), member.id);
+    }
+  }
 
   return membersMap;
 }
@@ -368,7 +382,7 @@
   jsonPrint,
   matchList,
   parseList,
-  createMemberMapForUserMentions,
+  useMemberMapForUserMentions,
   matchUserMentions,
   parseUserMentions,
   stripSpoilersFromNotifications,
diff --git a/native/markdown/rules.react.js b/native/markdown/rules.react.js
--- a/native/markdown/rules.react.js
+++ b/native/markdown/rules.react.js
@@ -363,12 +363,19 @@
   chatMentionCandidates: ChatMentionCandidates,
 ): (useDarkStyle: boolean) => MarkdownRules {
   const { members } = threadInfo;
+  const membersMap = SharedMarkdown.useMemberMapForUserMentions(members);
+
   return React.useMemo(
     () =>
       _memoize<[boolean], MarkdownRules>((useDarkStyle: boolean) =>
-        textMessageRules(members, chatMentionCandidates, useDarkStyle),
+        textMessageRules(
+          members,
+          chatMentionCandidates,
+          useDarkStyle,
+          membersMap,
+        ),
       ),
-    [members, chatMentionCandidates],
+    [members, chatMentionCandidates, membersMap],
   );
 }
 
@@ -376,9 +383,9 @@
   members: $ReadOnlyArray<RelativeMemberInfo>,
   chatMentionCandidates: ChatMentionCandidates,
   useDarkStyle: boolean,
+  membersMap: $ReadOnlyMap<string, string>,
 ): MarkdownRules {
   const baseRules = fullMarkdownRules(useDarkStyle);
-  const membersMap = SharedMarkdown.createMemberMapForUserMentions(members);
 
   return {
     ...baseRules,
@@ -428,15 +435,26 @@
 }
 
 let defaultTextMessageRules = null;
+const defaultMembersMap = new Map<string, string>();
 
 function getDefaultTextMessageRules(
   overrideDefaultChatMentionCandidates: ChatMentionCandidates = {},
 ): MarkdownRules {
   if (Object.keys(overrideDefaultChatMentionCandidates).length > 0) {
-    return textMessageRules([], overrideDefaultChatMentionCandidates, false);
+    return textMessageRules(
+      [],
+      overrideDefaultChatMentionCandidates,
+      false,
+      defaultMembersMap,
+    );
   }
   if (!defaultTextMessageRules) {
-    defaultTextMessageRules = textMessageRules([], {}, false);
+    defaultTextMessageRules = textMessageRules(
+      [],
+      {},
+      false,
+      defaultMembersMap,
+    );
   }
   return defaultTextMessageRules;
 }
diff --git a/web/markdown/rules.react.js b/web/markdown/rules.react.js
--- a/web/markdown/rules.react.js
+++ b/web/markdown/rules.react.js
@@ -169,12 +169,19 @@
   chatMentionCandidates: ChatMentionCandidates,
 ): boolean => MarkdownRules {
   const { members } = threadInfo;
+  const membersMap = SharedMarkdown.useMemberMapForUserMentions(members);
+
   return React.useMemo(
     () =>
       _memoize<[boolean], MarkdownRules>((useDarkStyle: boolean) =>
-        textMessageRules(members, chatMentionCandidates, useDarkStyle),
+        textMessageRules(
+          members,
+          chatMentionCandidates,
+          useDarkStyle,
+          membersMap,
+        ),
       ),
-    [chatMentionCandidates, members],
+    [chatMentionCandidates, members, membersMap],
   );
 }
 
@@ -182,9 +189,9 @@
   members: $ReadOnlyArray<RelativeMemberInfo>,
   chatMentionCandidates: ChatMentionCandidates,
   useDarkStyle: boolean,
+  membersMap: $ReadOnlyMap<string, string>,
 ): MarkdownRules {
   const baseRules = markdownRules(useDarkStyle);
-  const membersMap = SharedMarkdown.createMemberMapForUserMentions(members);
 
   return {
     ...baseRules,
@@ -232,15 +239,26 @@
 }
 
 let defaultTextMessageRules = null;
+const defaultMembersMap = new Map<string, string>();
 
 function getDefaultTextMessageRules(
   overrideDefaultChatMentionCandidates: ChatMentionCandidates = {},
 ): MarkdownRules {
   if (Object.keys(overrideDefaultChatMentionCandidates).length > 0) {
-    return textMessageRules([], overrideDefaultChatMentionCandidates, false);
+    return textMessageRules(
+      [],
+      overrideDefaultChatMentionCandidates,
+      false,
+      defaultMembersMap,
+    );
   }
   if (!defaultTextMessageRules) {
-    defaultTextMessageRules = textMessageRules([], {}, false);
+    defaultTextMessageRules = textMessageRules(
+      [],
+      {},
+      false,
+      defaultMembersMap,
+    );
   }
   return defaultTextMessageRules;
 }