diff --git a/lib/selectors/chat-selectors.js b/lib/selectors/chat-selectors.js
--- a/lib/selectors/chat-selectors.js
+++ b/lib/selectors/chat-selectors.js
@@ -272,6 +272,7 @@
   endsCluster: boolean,
   +robotext: string,
   +threadCreatedFromMessage: ?ThreadInfo,
+  +reactions: $ReadOnlyMap<string, MessageReactionInfo>,
 };
 export type ChatMessageInfoItem =
   | RobotextChatMessageInfoItem
@@ -283,8 +284,14 @@
       +startsCluster: boolean,
       endsCluster: boolean,
       +threadCreatedFromMessage: ?ThreadInfo,
+      +reactions: $ReadOnlyMap<string, MessageReactionInfo>,
     };
 export type ChatMessageItem = { itemType: 'loader' } | ChatMessageInfoItem;
+export type MessageReactionInfo = {
+  +viewerReacted: boolean,
+  +users: $ReadOnlySet<string>,
+};
+
 const msInFiveMinutes = 5 * 60 * 1000;
 function createChatMessageItems(
   threadID: string,
@@ -304,6 +311,81 @@
       ? sortMessageInfoList([...threadMessageInfos, ...additionalMessages])
       : threadMessageInfos;
 
+  const targetMessageReactionsMap = new Map<
+    string,
+    Map<
+      string,
+      {
+        +users: Set<string>,
+        viewerReacted: boolean,
+      },
+    >,
+  >();
+
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const messageInfo = messages[i];
+    if (messageInfo.type !== messageTypes.REACTION) {
+      continue;
+    }
+
+    if (!targetMessageReactionsMap.has(messageInfo.targetMessageID)) {
+      const reactsMap = new Map<
+        string,
+        {
+          +users: Set<string>,
+          viewerReacted: boolean,
+        },
+      >();
+
+      const usersSet = new Set<string>();
+      usersSet.add(JSON.stringify(messageInfo.creator));
+
+      const messageReactionInfo = {
+        viewerReacted: messageInfo.creator.isViewer,
+        users: usersSet,
+      };
+
+      reactsMap.set(messageInfo.reaction, messageReactionInfo);
+      targetMessageReactionsMap.set(messageInfo.targetMessageID, reactsMap);
+      continue;
+    }
+
+    const messageReactsMap = targetMessageReactionsMap.get(
+      messageInfo.targetMessageID,
+    );
+    invariant(messageReactsMap, 'messageReactsInfo should be set');
+
+    if (!messageReactsMap.has(messageInfo.reaction)) {
+      const usersSet = new Set<string>();
+      usersSet.add(JSON.stringify(messageInfo.creator));
+
+      const messageReactionInfo = {
+        viewerReacted: messageInfo.creator.isViewer,
+        users: usersSet,
+      };
+
+      messageReactsMap.set(messageInfo.reaction, messageReactionInfo);
+      continue;
+    }
+
+    const messageReactionInfo = messageReactsMap.get(messageInfo.reaction);
+    invariant(messageReactionInfo, 'specificReactionInfo should be set');
+
+    if (messageInfo.action === 'add_reaction') {
+      if (messageInfo.creator.isViewer) {
+        messageReactionInfo.viewerReacted = true;
+      }
+
+      messageReactionInfo.users.add(JSON.stringify(messageInfo.creator));
+    } else {
+      if (messageInfo.creator.isViewer) {
+        messageReactionInfo.viewerReacted = false;
+      }
+
+      messageReactionInfo.users.delete(JSON.stringify(messageInfo.creator));
+    }
+  }
+
   const chatMessageItems = [];
   let lastMessageInfo = null;
   for (let i = messages.length - 1; i >= 0; i--) {
@@ -346,6 +428,33 @@
       messageInfo.id && threadInfos[threadID]?.type !== threadTypes.SIDEBAR
         ? threadInfoFromSourceMessageID[messageInfo.id]
         : undefined;
+
+    const renderedReactions: $ReadOnlyMap<
+      string,
+      MessageReactionInfo,
+    > = (() => {
+      let result;
+
+      if (originalMessageInfo.id) {
+        result = targetMessageReactionsMap.get(originalMessageInfo.id);
+      }
+
+      if (!result) {
+        result = new Map<string, MessageReactionInfo>();
+      }
+
+      for (const reaction of result.keys()) {
+        const reactionInfo = result.get(reaction);
+        invariant(reactionInfo, 'reactionInfo should be set');
+
+        if (reactionInfo.users.size === 0) {
+          result.delete(reaction);
+        }
+      }
+
+      return result;
+    })();
+
     if (isComposableMessageType(originalMessageInfo.type)) {
       // We use these invariants instead of just checking the messageInfo.type
       // directly in the conditional above so that isComposableMessageType can
@@ -358,6 +467,7 @@
       );
       const localMessageInfo =
         messageStore.local[messageKey(originalMessageInfo)];
+
       chatMessageItems.push({
         itemType: 'message',
         messageInfo: originalMessageInfo,
@@ -366,6 +476,7 @@
         startsCluster,
         endsCluster: false,
         threadCreatedFromMessage,
+        reactions: renderedReactions,
       });
     } else {
       invariant(
@@ -386,6 +497,7 @@
         endsCluster: false,
         threadCreatedFromMessage,
         robotext,
+        reactions: renderedReactions,
       });
     }
     lastMessageInfo = originalMessageInfo;