diff --git a/packages/features/bookings/Booker/components/hooks/useSlots.ts b/packages/features/bookings/Booker/components/hooks/useSlots.ts
index faebef50984eec..1519e3550d722b 100644
--- a/packages/features/bookings/Booker/components/hooks/useSlots.ts
+++ b/packages/features/bookings/Booker/components/hooks/useSlots.ts
@@ -90,7 +90,10 @@ export const useSlots = (event: { id: number; length: number } | null) => {
       ],
       shallow
     );
-  const [slotReservationId, setSlotReservationId] = useSlotReservationId();
+  const [slotReservationId, setSlotReservationId] = useBookerStoreContext(
+    (state) => [state.slotReservationId, state.setSlotReservationId],
+    shallow
+  );
   const reserveSlotMutation = trpc.viewer.slots.reserveSlot.useMutation({
     trpc: {
       context: {
diff --git a/packages/features/bookings/Booker/store.ts b/packages/features/bookings/Booker/store.ts
index 39d97e5b405b67..0da6de8eab162a 100644
--- a/packages/features/bookings/Booker/store.ts
+++ b/packages/features/bookings/Booker/store.ts
@@ -154,6 +154,13 @@ export type BookerStore = {
    */
   formValues: Record<string, any>;
   setFormValues: (values: Record<string, any>) => void;
+  /**
+   * UID of the reserved slot. Used to prevent double-bookings by
+   * validating reservation ownership before creating a booking.
+   * Set when a slot is reserved, cleared after successful booking.
+   */
+  slotReservationId: string | null;
+  setSlotReservationId: (slotReservationId: string | null) => void;
   /**
    * Force event being a team event, so we only query for team events instead
    * of also include 'user' events and return the first event that matches with
@@ -437,6 +444,10 @@ export const createBookerStore = () =>
     setFormValues: (formValues: Record<string, any>) => {
       set({ formValues });
     },
+    slotReservationId: null,
+    setSlotReservationId: (slotReservationId: string | null) => {
+      set({ slotReservationId });
+    },
     org: null,
     setOrg: (org: string | null | undefined) => {
       set({ org });
diff --git a/packages/features/bookings/lib/book-event-form/booking-to-mutation-input-mapper.tsx b/packages/features/bookings/lib/book-event-form/booking-to-mutation-input-mapper.tsx
index caadc7c3e9d6b4..cf96bf325f84a1 100644
--- a/packages/features/bookings/lib/book-event-form/booking-to-mutation-input-mapper.tsx
+++ b/packages/features/bookings/lib/book-event-form/booking-to-mutation-input-mapper.tsx
@@ -32,6 +32,7 @@ export type BookingOptions = {
   routingFormSearchParams?: RoutingFormSearchParams;
   isDryRunProp?: boolean;
   verificationCode?: string;
+  reservedSlotUid?: string;
 };
 
 export const mapBookingToMutationInput = ({
@@ -56,6 +57,7 @@ export const mapBookingToMutationInput = ({
   routingFormSearchParams,
   isDryRunProp,
   verificationCode,
+  reservedSlotUid,
 }: BookingOptions): BookingCreateBody => {
   const searchParams = new URLSearchParams(routingFormSearchParams ?? window.location.search);
   const routedTeamMemberIds = getRoutedTeamMemberIdsFromSearchParams(searchParams);
@@ -101,6 +103,7 @@ export const mapBookingToMutationInput = ({
     _shouldServeCache,
     dub_id,
     verificationCode,
+    reservedSlotUid,
   };
 };
 
diff --git a/packages/features/bookings/lib/bookingCreateBodySchema.ts b/packages/features/bookings/lib/bookingCreateBodySchema.ts
index 9da43a92398edd..f1b6c7f247870d 100644
--- a/packages/features/bookings/lib/bookingCreateBodySchema.ts
+++ b/packages/features/bookings/lib/bookingCreateBodySchema.ts
@@ -53,6 +53,7 @@ export const bookingCreateBodySchema = z.object({
   dub_id: z.string().nullish(),
   creationSource: z.nativeEnum(CreationSource).optional(),
   verificationCode: z.string().optional(),
+  reservedSlotUid: z.string().optional(),
 });
 
 export type BookingCreateBody = z.input<typeof bookingCreateBodySchema>;
diff --git a/packages/features/bookings/lib/handleNewBooking.ts b/packages/features/bookings/lib/handleNewBooking.ts
index d473c146dd7b1f..6ce4652510dc27 100644
--- a/packages/features/bookings/lib/handleNewBooking.ts
+++ b/packages/features/bookings/lib/handleNewBooking.ts
@@ -62,6 +62,7 @@ import logger from "@calcom/lib/logger";
 import { getPiiFreeCalendarEvent, getPiiFreeEventType } from "@calcom/lib/piiFreeData";
 import { safeStringify } from "@calcom/lib/safeStringify";
 import { getTranslation } from "@calcom/lib/server/i18n";
+import { PrismaSelectedSlotRepository } from "@calcom/lib/server/repository/PrismaSelectedSlotRepository";
 import { BookingRepository } from "@calcom/lib/server/repository/booking";
 import { WorkflowRepository } from "@calcom/lib/server/repository/workflow";
 import { HashedLinkService } from "@calcom/lib/server/service/hashedLinkService";
@@ -485,6 +486,7 @@ async function handler(
     routingFormResponseId,
     _isDryRun: isDryRun = false,
     _shouldServeCache,
+    reservedSlotUid,
     ...reqBody
   } = bookingData;
 
@@ -839,6 +841,55 @@ async function handler(
     }
 
     if (!input.bookingData.allRecurringDates || input.bookingData.isFirstRecurringSlot) {
+      // Check for reserved slots - if reservedSlotUid is provided, verify this booking owns the reservation
+      // If no reservedSlotUid but slot is reserved by someone else, reject the booking
+      if (!isDryRun) {
+        const slotsRepo = new PrismaSelectedSlotRepository(prisma);
+        const slot = {
+          utcStartIso: dayjs(reqBody.start).utc().toISOString(),
+          utcEndIso: dayjs(reqBody.end).utc().toISOString(),
+        };
+
+        if (reservedSlotUid) {
+          // Check if this reservation still exists and belongs to this user
+          const reservation = await slotsRepo.findReservedByOthers({
+            slot,
+            eventTypeId,
+            uid: reservedSlotUid,
+          });
+
+          if (reservation) {
+            loggerWithEventDetails.error("Slot is reserved by someone else", {
+              reservedSlotUid,
+              eventTypeId,
+              slot,
+            });
+            throw new HttpError({
+              statusCode: 409,
+              message: "selected_timeslot_unavailable",
+            });
+          }
+        } else {
+          // Check if slot is reserved by anyone (for bookings without a reservation)
+          const reservation = await slotsRepo.findReservedByOthers({
+            slot,
+            eventTypeId,
+            uid: "dummy-uid-to-check-all-reservations",
+          });
+
+          if (reservation) {
+            loggerWithEventDetails.error("Slot is reserved by another user", {
+              eventTypeId,
+              slot,
+            });
+            throw new HttpError({
+              statusCode: 409,
+              message: "selected_timeslot_unavailable",
+            });
+          }
+        }
+      }
+
       try {
         if (!skipAvailabilityCheck) {
           availableUsers = await ensureAvailableUsers(
@@ -1590,6 +1641,30 @@ async function handler(
         }
       }
 
+      // Clean up reserved slot after successful booking creation
+      if (reservedSlotUid && booking) {
+        try {
+          await prisma.selectedSlots.deleteMany({
+            where: {
+              uid: reservedSlotUid,
+              eventTypeId,
+              slotUtcStartDate: dayjs(reqBody.start).utc().toDate(),
+              slotUtcEndDate: dayjs(reqBody.end).utc().toDate(),
+            },
+          });
+          loggerWithEventDetails.debug("Reserved slot deleted after booking creation", {
+            reservedSlotUid,
+            bookingUid: booking.uid,
+          });
+        } catch (error) {
+          // Log but don't fail the booking if slot cleanup fails
+          loggerWithEventDetails.warn("Failed to clean up reserved slot after booking creation", {
+            reservedSlotUid,
+            error,
+          });
+        }
+      }
+
       const updatedEvtWithUid = CalendarEventBuilder.fromEvent(evt)
         ?.withUid(booking.uid ?? null)
         .build();
diff --git a/packages/platform/atoms/hooks/bookings/useHandleBookEvent.ts b/packages/platform/atoms/hooks/bookings/useHandleBookEvent.ts
index 8260e05cb86cfc..ff1d1c55f7c751 100644
--- a/packages/platform/atoms/hooks/bookings/useHandleBookEvent.ts
+++ b/packages/platform/atoms/hooks/bookings/useHandleBookEvent.ts
@@ -64,6 +64,7 @@ export const useHandleBookEvent = ({
   const crmAppSlug = useBookerStoreContext((state) => state.crmAppSlug);
   const crmRecordId = useBookerStoreContext((state) => state.crmRecordId);
   const verificationCode = useBookerStoreContext((state) => state.verificationCode);
+  const slotReservationId = useBookerStoreContext((state) => state.slotReservationId);
   const handleError = (err: any) => {
     const errorMessage = err?.message ? t(err.message) : t("can_you_try_again");
     showToast(errorMessage, "error");
@@ -115,6 +116,7 @@ export const useHandleBookEvent = ({
         routingFormSearchParams,
         isDryRunProp: isBookingDryRun,
         verificationCode: verificationCode || undefined,
+        reservedSlotUid: slotReservationId || undefined,
       };
 
       const tracking = getUtmTrackingParameters(searchParams);
diff --git a/packages/platform/atoms/hooks/useSlots.ts b/packages/platform/atoms/hooks/useSlots.ts
index 005fad29b353d4..04b717b07d39f5 100644
--- a/packages/platform/atoms/hooks/useSlots.ts
+++ b/packages/platform/atoms/hooks/useSlots.ts
@@ -42,7 +42,10 @@ export const useSlots = (
     shallow
   );
 
-  const [slotReservationId, setSlotReservationId] = useSlotReservationId();
+  const [slotReservationId, setSlotReservationId] = useBookerStoreContext(
+    (state) => [state.slotReservationId, state.setSlotReservationId],
+    shallow
+  );
 
   const reserveSlotMutation = useReserveSlot({
     onSuccess: (res) => {