diff --git a/apps/backend/src/eventHandlers/email/emailTemplateId.ts b/apps/backend/src/eventHandlers/email/emailTemplateId.ts
index e83c8e0853..9a64fe2ca2 100644
--- a/apps/backend/src/eventHandlers/email/emailTemplateId.ts
+++ b/apps/backend/src/eventHandlers/email/emailTemplateId.ts
@@ -18,4 +18,5 @@ export enum EmailTemplateId {
   CALL_CREATED_EMAIL = 'call-created-email',
   FEEDBACK_REQUEST = 'feedback-request',
   CO_PROPOSER_INVITE = 'co-proposer-invite',
+  DATA_ACCESS_USER_ADDED = 'data-access-user-added',
 }
diff --git a/apps/backend/src/eventHandlers/email/essEmailHandler.ts b/apps/backend/src/eventHandlers/email/essEmailHandler.ts
index b75e1a0662..003f796d4c 100644
--- a/apps/backend/src/eventHandlers/email/essEmailHandler.ts
+++ b/apps/backend/src/eventHandlers/email/essEmailHandler.ts
@@ -350,6 +350,61 @@ export async function essEmailHandler(event: ApplicationEvent) {
       break;
     }
 
+    case Event.DATA_ACCESS_USERS_UPDATED: {
+      // Only newly added users are notified; a pure removal or no-op update
+      // carries an empty list and sends nothing.
+      if (event.newlyAddedUserIds.length === 0) {
+        return;
+      }
+
+      const proposal = await proposalDataSource.get(event.proposalPKey);
+      if (!proposal) {
+        logger.logError('No proposal found when trying to send email', {
+          proposalPKey: event.proposalPKey,
+          event,
+        });
+
+        return;
+      }
+
+      const invitedUsers = await userDataSource.getBasicUsersInfo(
+        event.newlyAddedUserIds
+      );
+
+      for (const user of invitedUsers) {
+        mailService
+          .sendMail({
+            content: {
+              template: EmailTemplateId.DATA_ACCESS_USER_ADDED,
+            },
+            substitution_data: {
+              preferredname: user.preferredname,
+              firstname: user.firstname,
+              lastname: user.lastname,
+              proposalTitle: proposal.title,
+              proposalId: proposal.proposalId,
+            },
+            recipients: [{ address: user.email }],
+          })
+          .then((res) => {
+            logger.logInfo('Email sent on data access user added', {
+              result: res,
+              userId: user.id,
+              proposalPKey: event.proposalPKey,
+            });
+          })
+          .catch((err: string) => {
+            logger.logError('Could not send email on data access user added', {
+              error: err,
+              userId: user.id,
+              event,
+            });
+          });
+      }
+
+      return;
+    }
+
     case Event.FAP_REVIEWER_NOTIFIED: {
       const { id: reviewId, userID, proposalPk } = event.fapReview;
       const fapReviewer = await userDataSource.getUser(userID);
diff --git a/apps/backend/src/events/applicationEvents.ts b/apps/backend/src/events/applicationEvents.ts
index 7322996f46..c4b51b32d6 100644
--- a/apps/backend/src/events/applicationEvents.ts
+++ b/apps/backend/src/events/applicationEvents.ts
@@ -420,6 +420,9 @@ interface VisitRegistrationCancelledEvent extends GeneralEvent {
 interface UserDataAccessUpdatedEvent extends GeneralEvent {
   type: Event.DATA_ACCESS_USERS_UPDATED;
   proposalPKey: number;
+  // Users newly added as data access users in this update (empty on removals
+  // or no-op updates). Used to notify only the freshly invited users by email.
+  newlyAddedUserIds: number[];
 }
 
 interface ExperimentSafetyManagementDecisionSubmittedByISEvent
diff --git a/apps/backend/src/mutations/DataAccessUsersMutations.ts b/apps/backend/src/mutations/DataAccessUsersMutations.ts
index 147355e382..1557ec06be 100644
--- a/apps/backend/src/mutations/DataAccessUsersMutations.ts
+++ b/apps/backend/src/mutations/DataAccessUsersMutations.ts
@@ -58,6 +58,17 @@ export default class DataAccessUsersMutations {
         );
       }
 
+      // Data access users are stored via delete-all + reinsert, so capture the
+      // current members first to work out who is genuinely newly invited.
+      const existingDataAccessUsers =
+        await this.dataSource.findByProposalPk(proposalPk);
+      const existingUserIds = new Set(
+        existingDataAccessUsers.map((user) => user.id)
+      );
+      const newlyAddedUserIds = userIds.filter(
+        (userId) => !existingUserIds.has(userId)
+      );
+
       const result = await this.dataSource.updateDataAccessUsers(
         proposalPk,
         userIds
@@ -69,6 +80,7 @@ export default class DataAccessUsersMutations {
         await eventBus.publish({
           type: Event.DATA_ACCESS_USERS_UPDATED,
           proposalPKey: proposalPk,
+          newlyAddedUserIds: newlyAddedUserIds,
           key: 'proposalPk',
           loggedInUserId: agent ? agent.id : null,
           isRejection: false,