diff --git a/web/roles/create-roles-modal.css b/web/roles/create-roles-modal.css
--- a/web/roles/create-roles-modal.css
+++ b/web/roles/create-roles-modal.css
@@ -16,6 +16,17 @@
   margin: 8px 0 12px 0;
 }
 
+.errorMessage {
+  color: var(--error);
+  font-size: var(--s-font-14);
+  align-self: center;
+  visibility: hidden;
+}
+
+.errorMessageVisible {
+  visibility: visible;
+}
+
 .separator {
   border: 0;
   margin: 16px 32px 8px 32px;
diff --git a/web/roles/create-roles-modal.react.js b/web/roles/create-roles-modal.react.js
--- a/web/roles/create-roles-modal.react.js
+++ b/web/roles/create-roles-modal.react.js
@@ -16,6 +16,7 @@
   useServerCall,
   useDispatchActionPromise,
 } from 'lib/utils/action-utils.js';
+import { values } from 'lib/utils/objects.js';
 
 import css from './create-roles-modal.css';
 import {
@@ -42,6 +43,8 @@
   +rolePermissions: $ReadOnlyArray<UserSurfacedPermission>,
 };
 
+type RoleCreationErrorVariant = 'already_exists' | 'unknown_error';
+
 function CreateRolesModal(props: CreateRolesModalProps): React.Node {
   const { pushModal, popModal } = useModalContext();
   const { threadInfo, action, existingRoleID, roleName, rolePermissions } =
@@ -59,8 +62,12 @@
   const [pendingRolePermissions, setPendingRolePermissions] =
     React.useState<$ReadOnlyArray<UserSurfacedPermission>>(rolePermissions);
 
+  const [roleCreationFailed, setRoleCreationFailed] =
+    React.useState<?RoleCreationErrorVariant>();
+
   const onChangeRoleName = React.useCallback(
     (event: SyntheticEvent<HTMLInputElement>) => {
+      setRoleCreationFailed(null);
       setPendingRoleName(event.currentTarget.value);
     },
     [],
@@ -152,13 +159,21 @@
     ],
   );
 
+  const errorMessageClassNames = classNames({
+    [css.errorMessage]: true,
+    [css.errorMessageVisible]: !!roleCreationFailed,
+  });
+
   const onClickCreateRole = React.useCallback(() => {
-    // TODO: Error handling in a later diff
+    const threadRoleNames = values(threadInfo.roles).map(role => role.name);
+    if (threadRoleNames.includes(pendingRoleName) && action === 'create_role') {
+      setRoleCreationFailed('already_exists');
+      return;
+    }
 
     dispatchActionPromise(
       modifyCommunityRoleActionTypes,
       (async () => {
-        //eslint-disable-next-line no-useless-catch
         try {
           const response = await callModifyCommunityRole({
             community: threadInfo.id,
@@ -170,6 +185,7 @@
           popModal();
           return response;
         } catch (e) {
+          setRoleCreationFailed('unknown_error');
           throw e;
         }
       })(),
@@ -185,6 +201,16 @@
     popModal,
   ]);
 
+  const errorMessage = React.useMemo(() => {
+    if (roleCreationFailed === 'already_exists') {
+      return 'There is already a role with this name in the community';
+    } else if (roleCreationFailed === 'unknown_error') {
+      return 'An unknown error occurred. Please try again';
+    } else {
+      return 'An unknown error occurred. Please try again';
+    }
+  }, [roleCreationFailed]);
+
   const saveButtonContent = React.useMemo(() => {
     if (createRolesLoadingStatus === 'loading') {
       return (
@@ -206,6 +232,7 @@
             onChange={onChangeRoleName}
           />
         </div>
+        <div className={errorMessageClassNames}>{errorMessage}</div>
       </form>
       <hr className={css.separator} />
       <div className={css.permissionsHeaderContainer}>