diff --git a/packages/base-data-service/CHANGELOG.md b/packages/base-data-service/CHANGELOG.md
index c3b10e0015..0e6fa4d503 100644
--- a/packages/base-data-service/CHANGELOG.md
+++ b/packages/base-data-service/CHANGELOG.md
@@ -46,6 +46,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Bump `@metamask/messenger` from `^1.2.0` to `^2.0.0` ([#9392](https://github.com/MetaMask/core/pull/9392))
 - Add dependency `cockatiel` (`^3.1.2`) ([#9418](https://github.com/MetaMask/core/pull/9418))
 
+### Fixed
+
+- Prevent `fetchInfiniteQuery` from duplicating a page when re-fetching a page param that is already present in the cache ([#9915](https://github.com/MetaMask/core/pull/9915), [#9900](https://github.com/MetaMask/core/issues/9900))
+  - The fresh page now replaces the cached one in place instead of being appended or prepended, which previously left duplicate, out-of-order pages in the cache.
+
 ## [0.1.3]
 
 ### Changed
diff --git a/packages/base-data-service/src/BaseDataService.test.ts b/packages/base-data-service/src/BaseDataService.test.ts
index 152eb6bd81..d0add6ac36 100644
--- a/packages/base-data-service/src/BaseDataService.test.ts
+++ b/packages/base-data-service/src/BaseDataService.test.ts
@@ -121,6 +121,100 @@ describe('BaseDataService', () => {
     expect(page2.data).not.toStrictEqual(page3.data);
   });
 
+  it('replaces an already-cached page in place when fetching it again', async () => {
+    cleanAll();
+    const messenger = new Messenger({ namespace: serviceName });
+    const service = new ExampleDataService(messenger);
+    const publishSpy = jest.spyOn(messenger, 'publish');
+
+    const page2Body = {
+      data: [
+        {
+          hash: '0xcecd28aa5bd781ffd2a6d960578ffc6c89ac390e8d02baebc977a827956394e9',
+          timestamp: '2025-12-29T11:51:08.000Z',
+        },
+      ],
+      pageInfo: {
+        count: 1,
+        hasNextPage: false,
+        hasPreviousPage: true,
+        startCursor: 'page1-cursor',
+        endCursor: 'page3-cursor',
+      },
+    };
+    mockTransactionsPage2({ status: 200, body: page2Body });
+    mockTransactionsPage2({ status: 200, body: page2Body });
+
+    const page2 = await service.getActivity(TEST_ADDRESS, {
+      after: TRANSACTIONS_PAGE_2_CURSOR,
+    });
+    expect(page2.data).toHaveLength(1);
+
+    // A refetch re-requests a page that is already present in the cache.
+    const page2Again = await service.getActivity(TEST_ADDRESS, {
+      after: TRANSACTIONS_PAGE_2_CURSOR,
+    });
+    expect(page2Again.data).toStrictEqual(page2.data);
+
+    const queryKey = ['ExampleDataService:getActivity', TEST_ADDRESS];
+    const hash = hashKey(queryKey);
+    const cacheUpdate = publishSpy.mock.calls
+      .filter(([event]) => event === `ExampleDataService:cacheUpdated:${hash}`)
+      .at(-1)?.[1] as {
+      state: { queries: [{ state: { data: { pages: unknown[] } } }] };
+    };
+
+    // The cache must hold each page exactly once.
+    expect(cacheUpdate.state.queries[0].state.data.pages).toHaveLength(1);
+  });
+
+  it('replaces an already-cached page in place when fetching it again in the forward direction', async () => {
+    cleanAll();
+    const messenger = new Messenger({ namespace: serviceName });
+    const service = new ExampleDataService(messenger);
+    const publishSpy = jest.spyOn(messenger, 'publish');
+
+    const page2Body = {
+      data: [
+        {
+          hash: '0xcecd28aa5bd781ffd2a6d960578ffc6c89ac390e8d02baebc977a827956394e9',
+          timestamp: '2025-12-29T11:51:08.000Z',
+        },
+      ],
+      pageInfo: {
+        count: 1,
+        hasNextPage: true,
+        hasPreviousPage: false,
+        startCursor: null,
+        endCursor: TRANSACTIONS_PAGE_2_CURSOR,
+      },
+    };
+    mockTransactionsPage2({ status: 200, body: page2Body });
+    mockTransactionsPage2({ status: 200, body: page2Body });
+
+    const page2 = await service.getActivity(TEST_ADDRESS, {
+      after: TRANSACTIONS_PAGE_2_CURSOR,
+    });
+    expect(page2.data).toHaveLength(1);
+
+    // A refetch re-requests a page that is already present in the cache.
+    const page2Again = await service.getActivity(TEST_ADDRESS, {
+      after: TRANSACTIONS_PAGE_2_CURSOR,
+    });
+    expect(page2Again.data).toStrictEqual(page2.data);
+
+    const queryKey = ['ExampleDataService:getActivity', TEST_ADDRESS];
+    const hash = hashKey(queryKey);
+    const cacheUpdate = publishSpy.mock.calls
+      .filter(([event]) => event === `ExampleDataService:cacheUpdated:${hash}`)
+      .at(-1)?.[1] as {
+      state: { queries: [{ state: { data: { pages: unknown[] } } }] };
+    };
+
+    // The cache must hold each page exactly once.
+    expect(cacheUpdate.state.queries[0].state.data.pages).toHaveLength(1);
+  });
+
   it('emits `:cacheUpdated` events when cache is updated', async () => {
     const messenger = new Messenger({ namespace: serviceName });
     const service = new ExampleDataService(messenger);
diff --git a/packages/base-data-service/src/BaseDataService.ts b/packages/base-data-service/src/BaseDataService.ts
index d0d419f65c..ba2cbf7596 100644
--- a/packages/base-data-service/src/BaseDataService.ts
+++ b/packages/base-data-service/src/BaseDataService.ts
@@ -333,6 +333,11 @@ export class BaseDataService<
     }
 
     const { pages, pageParams } = query.state.data;
+
+    const existingIndex = pageParams.findIndex((param) =>
+      deepEqual(param, pageParam),
+    );
+
     const next = options.getNextPageParam(
       pages[pages.length - 1],
       pages,
@@ -347,6 +352,28 @@ export class BaseDataService<
       { meta: { fetchMore: { direction } } },
     );
 
+    if (existingIndex !== -1) {
+      // The requested page was already cached. `query.fetch` appended or
+      // prepended a fresh copy instead of replacing it, which would leave
+      // duplicate, out-of-order pages in the cache. Collapse the duplicate
+      // and keep the fresh page at the original position.
+      const isForward = direction === 'forward';
+      const nextPages = [...result.pages];
+      const nextPageParams = [...result.pageParams];
+      const freshPage = isForward ? nextPages.pop() : nextPages.shift();
+      if (isForward) {
+        nextPageParams.pop();
+      } else {
+        nextPageParams.shift();
+      }
+      nextPages[existingIndex] = freshPage as TData;
+      this.#queryClient.setQueryData(options.queryKey, {
+        pages: nextPages,
+        pageParams: nextPageParams,
+      });
+      return freshPage as TData;
+    }
+
     const pageIndex = result.pageParams.findIndex((param) =>
       deepEqual(param, pageParam),
     );