diff --git a/integration-tests/modules/__tests__/cart/store/carts.spec.ts b/integration-tests/modules/__tests__/cart/store/carts.spec.ts
index cb68389932..ab1aed0098 100644
--- a/integration-tests/modules/__tests__/cart/store/carts.spec.ts
+++ b/integration-tests/modules/__tests__/cart/store/carts.spec.ts
@@ -1972,6 +1972,10 @@ medusaIntegrationTestRunner({
           )
         })
 
+        afterEach(async () => {
+          jest.clearAllMocks()
+        })
+
         it("should create an order and create item reservations", async () => {
           const cart = (
             await api.post(`/store/carts`, {
@@ -2136,6 +2140,62 @@ medusaIntegrationTestRunner({
           })
         })
 
+        it("should fail to update cart when it is completed", async () => {
+          const cart = (
+            await api.post(`/store/carts`, {
+              currency_code: "usd",
+              email: "tony@stark-industries.com",
+              shipping_address: {
+                address_1: "test address 1",
+                address_2: "test address 2",
+                city: "ny",
+                country_code: "us",
+                province: "ny",
+                postal_code: "94016",
+              },
+              sales_channel_id: salesChannel.id,
+              items: [{ quantity: 1, variant_id: product.variants[0].id }],
+            })
+          ).data.cart
+
+          const paymentCollection = (
+            await api.post(`/store/payment-collections`, {
+              cart_id: cart.id,
+            })
+          ).data.payment_collection
+
+          await api.post(
+            `/store/payment-collections/${paymentCollection.id}/payment-sessions`,
+            { provider_id: "pp_system_default" }
+          )
+
+          await api.post(`/store/carts/${cart.id}/complete`, {})
+
+          const cartRefetch = (await api.get(`/store/carts/${cart.id}`)).data
+            .cart
+
+          expect(cartRefetch.completed_at).toBeTruthy()
+
+          await expect(
+            api.post(`/store/carts/${cart.id}/shipping-methods`, {
+              option_id: shippingOption.id,
+            })
+          ).rejects.toThrow()
+
+          const error = await api
+            .post(`/store/carts/${cart.id}/line-items`, {
+              variant_id: product.variants[0].id,
+              quantity: 1,
+            })
+            .catch((e) => e)
+
+          expect(error.response.status).toEqual(400)
+          expect(error.response.data).toEqual({
+            type: "invalid_data",
+            message: `Cart ${cart.id} is already completed.`,
+          })
+        })
+
         it("should return cart when payment authorization fails", async () => {
           const authorizePaymentSessionSpy = jest.spyOn(
             PaymentModuleService.prototype,
diff --git a/packages/core/core-flows/src/cart/steps/validate-cart.ts b/packages/core/core-flows/src/cart/steps/validate-cart.ts
new file mode 100644
index 0000000000..b4115f3901
--- /dev/null
+++ b/packages/core/core-flows/src/cart/steps/validate-cart.ts
@@ -0,0 +1,32 @@
+import { CartDTO, CartWorkflowDTO } from "@medusajs/types"
+import { MedusaError, isPresent } from "@medusajs/utils"
+import { createStep } from "@medusajs/workflows-sdk"
+
+export interface ValidateCartStepInput {
+  cart: CartWorkflowDTO | CartDTO
+}
+
+export const validateCartStepId = "validate-cart"
+/**
+ * This step validates a cart's before editing it.
+ */
+export const validateCartStep = createStep(
+  validateCartStepId,
+  async (data: ValidateCartStepInput) => {
+    const { cart } = data
+
+    if (!isPresent(cart)) {
+      throw new MedusaError(
+        MedusaError.Types.INVALID_DATA,
+        `Cart does not exist`
+      )
+    }
+
+    if (cart.completed_at) {
+      throw new MedusaError(
+        MedusaError.Types.INVALID_DATA,
+        `Cart ${cart.id} is already completed.`
+      )
+    }
+  }
+)
diff --git a/packages/core/core-flows/src/cart/utils/fields.ts b/packages/core/core-flows/src/cart/utils/fields.ts
index 44c41bc19c..bb804db7f7 100644
--- a/packages/core/core-flows/src/cart/utils/fields.ts
+++ b/packages/core/core-flows/src/cart/utils/fields.ts
@@ -1,9 +1,11 @@
 export const cartFieldsForRefreshSteps = [
+  "id",
   "subtotal",
   "item_subtotal",
   "shipping_subtotal",
   "region_id",
   "currency_code",
+  "completed_at",
   "region.*",
   "items.*",
   "items.product.id",
@@ -26,6 +28,7 @@ export const completeCartFields = [
   "email",
   "created_at",
   "updated_at",
+  "completed_at",
   "total",
   "subtotal",
   "tax_total",
diff --git a/packages/core/core-flows/src/cart/workflows/add-shipping-method-to-cart.ts b/packages/core/core-flows/src/cart/workflows/add-shipping-method-to-cart.ts
index 66b20bda4e..4afa9f3669 100644
--- a/packages/core/core-flows/src/cart/workflows/add-shipping-method-to-cart.ts
+++ b/packages/core/core-flows/src/cart/workflows/add-shipping-method-to-cart.ts
@@ -9,6 +9,7 @@ import {
   removeShippingMethodFromCartStep,
   validateCartShippingOptionsStep,
 } from "../steps"
+import { validateCartStep } from "../steps/validate-cart"
 import { cartFieldsForRefreshSteps } from "../utils/fields"
 import { updateCartPromotionsWorkflow } from "./update-cart-promotions"
 import { updateTaxLinesWorkflow } from "./update-tax-lines"
@@ -37,6 +38,8 @@ export const addShippingMethodToWorkflow = createWorkflow(
       list: false,
     })
 
+    validateCartStep({ cart })
+
     const optionIds = transform({ input }, (data) => {
       return (data.input.options ?? []).map((i) => i.id)
     })
diff --git a/packages/core/core-flows/src/cart/workflows/add-to-cart.ts b/packages/core/core-flows/src/cart/workflows/add-to-cart.ts
index f3b4caf68f..1e7a816999 100644
--- a/packages/core/core-flows/src/cart/workflows/add-to-cart.ts
+++ b/packages/core/core-flows/src/cart/workflows/add-to-cart.ts
@@ -16,6 +16,7 @@ import {
   refreshCartShippingMethodsStep,
   updateLineItemsStep,
 } from "../steps"
+import { validateCartStep } from "../steps/validate-cart"
 import { validateVariantPricesStep } from "../steps/validate-variant-prices"
 import {
   cartFieldsForRefreshSteps,
@@ -34,6 +35,8 @@ export const addToCartWorkflowId = "add-to-cart"
 export const addToCartWorkflow = createWorkflow(
   addToCartWorkflowId,
   (input: WorkflowData<AddToCartWorkflowInputDTO>) => {
+    validateCartStep(input)
+
     const variantIds = transform({ input }, (data) => {
       return (data.input.items ?? []).map((i) => i.variant_id)
     })
@@ -67,9 +70,10 @@ export const addToCartWorkflow = createWorkflow(
 
         return prepareLineItemData({
           variant: variant,
-          unitPrice: item.unit_price || 
-            variant.calculated_price.calculated_amount,
-          isTaxInclusive: item.is_tax_inclusive || 
+          unitPrice:
+            item.unit_price || variant.calculated_price.calculated_amount,
+          isTaxInclusive:
+            item.is_tax_inclusive ||
             variant.calculated_price.is_calculated_price_tax_inclusive,
           quantity: item.quantity,
           metadata: item?.metadata ?? {},
diff --git a/packages/core/core-flows/src/cart/workflows/complete-cart.ts b/packages/core/core-flows/src/cart/workflows/complete-cart.ts
index 17d9550068..fd1032c4e4 100644
--- a/packages/core/core-flows/src/cart/workflows/complete-cart.ts
+++ b/packages/core/core-flows/src/cart/workflows/complete-cart.ts
@@ -14,8 +14,9 @@ import {
 } from "../../common"
 import { createOrdersStep } from "../../order/steps/create-orders"
 import { authorizePaymentSessionStep } from "../../payment/steps/authorize-payment-session"
-import { validateCartPaymentsStep } from "../steps"
+import { updateCartsStep, validateCartPaymentsStep } from "../steps"
 import { reserveInventoryStep } from "../steps/reserve-inventory"
+import { validateCartStep } from "../steps/validate-cart"
 import { completeCartFields } from "../utils/fields"
 import { prepareConfirmInventoryInput } from "../utils/prepare-confirm-inventory-input"
 import {
@@ -44,6 +45,8 @@ export const completeCartWorkflow = createWorkflow(
       list: false,
     })
 
+    validateCartStep({ cart })
+
     const paymentSessions = validateCartPaymentsStep({ cart })
 
     authorizePaymentSessionStep({
@@ -158,6 +161,13 @@ export const completeCartWorkflow = createWorkflow(
       ({ createdOrders }) => createdOrders[0]
     )
 
+    const updateCompletedAt = transform({ cart }, ({ cart }) => {
+      return {
+        id: cart.id,
+        completed_at: new Date(),
+      }
+    })
+
     parallelize(
       createRemoteLinkStep([
         {
@@ -171,6 +181,7 @@ export const completeCartWorkflow = createWorkflow(
           },
         },
       ]),
+      updateCartsStep([updateCompletedAt]),
       emitEventStep({
         eventName: OrderWorkflowEvents.PLACED,
         data: { id: order.id },
diff --git a/packages/core/core-flows/src/cart/workflows/create-payment-collection-for-cart.ts b/packages/core/core-flows/src/cart/workflows/create-payment-collection-for-cart.ts
index 723f851479..1c7052bfa1 100644
--- a/packages/core/core-flows/src/cart/workflows/create-payment-collection-for-cart.ts
+++ b/packages/core/core-flows/src/cart/workflows/create-payment-collection-for-cart.ts
@@ -12,6 +12,7 @@ import {
 import { createRemoteLinkStep } from "../../common/steps/create-remote-links"
 import { useRemoteQueryStep } from "../../common/steps/use-remote-query"
 import { createPaymentCollectionsStep } from "../steps/create-payment-collection"
+import { validateCartStep } from "../steps/validate-cart"
 
 /**
  * This step validates that a cart doesn't have a payment collection.
@@ -40,6 +41,7 @@ export const createPaymentCollectionForCartWorkflow = createWorkflow(
       fields: [
         "id",
         "region_id",
+        "completed_at",
         "currency_code",
         "total",
         "raw_total",
@@ -50,6 +52,8 @@ export const createPaymentCollectionForCartWorkflow = createWorkflow(
       list: false,
     })
 
+    validateCartStep({ cart })
+
     validateExistingPaymentCollectionStep({ cart })
 
     const paymentData = transform({ cart }, ({ cart }) => {
diff --git a/packages/core/core-flows/src/cart/workflows/update-line-item-in-cart.ts b/packages/core/core-flows/src/cart/workflows/update-line-item-in-cart.ts
index 51c23396d3..fd578d2908 100644
--- a/packages/core/core-flows/src/cart/workflows/update-line-item-in-cart.ts
+++ b/packages/core/core-flows/src/cart/workflows/update-line-item-in-cart.ts
@@ -8,6 +8,7 @@ import {
 import { useRemoteQueryStep } from "../../common/steps/use-remote-query"
 import { updateLineItemsStepWithSelector } from "../../line-item/steps"
 import { refreshCartShippingMethodsStep } from "../steps"
+import { validateCartStep } from "../steps/validate-cart"
 import { validateVariantPricesStep } from "../steps/validate-variant-prices"
 import {
   cartFieldsForRefreshSteps,
@@ -27,6 +28,8 @@ export const updateLineItemInCartWorkflowId = "update-line-item-in-cart"
 export const updateLineItemInCartWorkflow = createWorkflow(
   updateLineItemInCartWorkflowId,
   (input: WorkflowData<UpdateLineItemInCartWorkflowInputDTO>) => {
+    validateCartStep(input)
+
     const variantIds = transform({ input }, (data) => {
       return [data.input.item.variant_id]
     })
diff --git a/packages/core/types/src/cart/common.ts b/packages/core/types/src/cart/common.ts
index d2bfc9f0a9..9bca584517 100644
--- a/packages/core/types/src/cart/common.ts
+++ b/packages/core/types/src/cart/common.ts
@@ -782,6 +782,11 @@ export interface CartDTO {
    */
   metadata?: Record<string, unknown> | null
 
+  /**
+   * When the cart was completed.
+   */
+  completed_at?: string | Date
+
   /**
    * When the cart was created.
    */
diff --git a/packages/medusa/src/api/store/carts/query-config.ts b/packages/medusa/src/api/store/carts/query-config.ts
index dee9cf5300..658ee7d49b 100644
--- a/packages/medusa/src/api/store/carts/query-config.ts
+++ b/packages/medusa/src/api/store/carts/query-config.ts
@@ -4,6 +4,7 @@ export const defaultStoreCartFields = [
   "email",
   "created_at",
   "updated_at",
+  "completed_at",
   "total",
   "subtotal",
   "tax_total",
diff --git a/packages/modules/cart/src/migrations/Migration20240831125857.ts b/packages/modules/cart/src/migrations/Migration20240831125857.ts
new file mode 100644
index 0000000000..b3024fb75c
--- /dev/null
+++ b/packages/modules/cart/src/migrations/Migration20240831125857.ts
@@ -0,0 +1,15 @@
+import { Migration } from "@mikro-orm/migrations"
+
+export class Migration20240831125857 extends Migration {
+  async up(): Promise<void> {
+    this.addSql(
+      'alter table if exists "cart" add column if not exists "completed_at" timestamptz null;'
+    )
+  }
+
+  async down(): Promise<void> {
+    this.addSql(
+      'alter table if exists "cart" drop column if exists "completed_at";'
+    )
+  }
+}
diff --git a/packages/modules/cart/src/models/cart.ts b/packages/modules/cart/src/models/cart.ts
index 99a92853f1..41f2236258 100644
--- a/packages/modules/cart/src/models/cart.ts
+++ b/packages/modules/cart/src/models/cart.ts
@@ -147,6 +147,9 @@ export default class Cart {
   })
   shipping_methods = new Collection<Rel<ShippingMethod>>(this)
 
+  @Property({ columnType: "timestamptz", nullable: true })
+  completed_at: Date | null = null
+
   @Property({
     onCreate: () => new Date(),
     columnType: "timestamptz",