diff --git a/.changeset/fix-concurrent-on-submit.md b/.changeset/fix-concurrent-on-submit.md
new file mode 100644
index 0000000000..5264c47e44
--- /dev/null
+++ b/.changeset/fix-concurrent-on-submit.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+fix(form-core): prevent concurrent onSubmit invocations while a submission is in progress
diff --git a/packages/form-core/src/FormApi.ts b/packages/form-core/src/FormApi.ts
index 4400017d30..91460f3d52 100644
--- a/packages/form-core/src/FormApi.ts
+++ b/packages/form-core/src/FormApi.ts
@@ -2448,8 +2448,12 @@ export class FormApi<
       // validateAllFields can re-run and clear stale field errors (e.g. from a
       // previous onBlur validation that is no longer relevant). The
       // isFieldsValid check below will call onSubmitInvalid if the form is
-      // still invalid after re-validation.
-      if (this.baseStore.state.submissionAttempts <= 1) {
+      // still invalid after re-validation. A submission that is already in
+      // progress always returns early so onSubmit cannot run concurrently.
+      if (
+        this.baseStore.state.submissionAttempts <= 1 ||
+        this.state.isSubmitting
+      ) {
         this.options.onSubmitInvalid?.({
           value: this.state.values,
           formApi: this,
diff --git a/packages/form-core/tests/FormApi.spec.ts b/packages/form-core/tests/FormApi.spec.ts
index c57bb044e8..943d3a53da 100644
--- a/packages/form-core/tests/FormApi.spec.ts
+++ b/packages/form-core/tests/FormApi.spec.ts
@@ -1991,6 +1991,33 @@ describe('form api', () => {
     expect(onSubmitInvalid).toHaveBeenCalledTimes(1) // not called again
   })
 
+  it('should not invoke onSubmit again while a submission is in progress', async () => {
+    vi.useRealTimers()
+    // Regression: once submissionAttempts > 1 the re-submission guard skipped
+    // the canSubmit early return, so each submit call during a pending
+    // submission invoked onSubmit again, causing concurrent submissions.
+    const onSubmit = vi.fn(async () => {
+      await sleep(500)
+    })
+    const onSubmitInvalid = vi.fn()
+
+    const form = new FormApi({
+      defaultValues: { firstName: 'test' },
+      onSubmit,
+      onSubmitInvalid,
+    })
+    form.mount()
+
+    const first = form.handleSubmit()
+    // Further submit attempts while the first submission is still pending
+    const second = form.handleSubmit()
+    const third = form.handleSubmit()
+    await Promise.all([first, second, third])
+
+    expect(onSubmit).toHaveBeenCalledTimes(1)
+    expect(onSubmitInvalid).toHaveBeenCalledTimes(2)
+  })
+
   it('should run all types of async validation on fields during submit', async () => {
     vi.useFakeTimers()