diff --git a/web/app.react.js b/web/app.react.js
--- a/web/app.react.js
+++ b/web/app.react.js
@@ -42,6 +42,7 @@
 import Calendar from './calendar/calendar.react.js';
 import Chat from './chat/chat.react.js';
 import { EditModalProvider } from './chat/edit-message-provider.js';
+import { MemberListSidebarProvider } from './chat/member-list-sidebar/member-list-sidebar-provider.react.js';
 import NavigationArrows from './components/navigation-arrows.react.js';
 import { initOpaque } from './crypto/opaque-utils.js';
 import { getDatabaseModule } from './database/database-module-provider.js';
@@ -191,8 +192,10 @@
           <WebEditThreadAvatarProvider>
             <EditUserAvatarProvider>
               <StaffContextProvider>
-                {this.renderMainContent()}
-                {this.props.modals}
+                <MemberListSidebarProvider>
+                  {this.renderMainContent()}
+                  {this.props.modals}
+                </MemberListSidebarProvider>
               </StaffContextProvider>
             </EditUserAvatarProvider>
           </WebEditThreadAvatarProvider>
diff --git a/web/chat/member-list-sidebar/member-list-sidebar-provider.react.js b/web/chat/member-list-sidebar/member-list-sidebar-provider.react.js
new file mode 100644
--- /dev/null
+++ b/web/chat/member-list-sidebar/member-list-sidebar-provider.react.js
@@ -0,0 +1,48 @@
+// @flow
+
+import invariant from 'invariant';
+import * as React from 'react';
+
+import type { SetState } from 'lib/types/hook-types.js';
+
+export type MemberListSidebarContextType = {
+  +showMemberListSidebar: boolean,
+  +setShowMemberListSidebar: SetState<boolean>,
+};
+
+const MemberListSidebarContext: React.Context<?MemberListSidebarContextType> =
+  React.createContext<?MemberListSidebarContextType>();
+
+type Props = {
+  +children: React.Node,
+};
+
+function MemberListSidebarProvider(props: Props): React.Node {
+  const { children } = props;
+
+  const [showMemberListSidebar, setShowMemberListSidebar] =
+    React.useState(false);
+
+  const contextValue = React.useMemo(
+    () => ({
+      showMemberListSidebar,
+      setShowMemberListSidebar,
+    }),
+    [showMemberListSidebar],
+  );
+
+  return (
+    <MemberListSidebarContext.Provider value={contextValue}>
+      {children}
+    </MemberListSidebarContext.Provider>
+  );
+}
+
+function useMemberListSidebarContext(): MemberListSidebarContextType {
+  const memberListSidebarContext = React.useContext(MemberListSidebarContext);
+
+  invariant(memberListSidebarContext, 'memberListSidebarContext should be set');
+  return memberListSidebarContext;
+}
+
+export { MemberListSidebarProvider, useMemberListSidebarContext };