diff --git a/src/webui/features/tasks/api/cancel-task.ts b/src/webui/features/tasks/api/cancel-task.ts
new file mode 100644
index 000000000..174414484
--- /dev/null
+++ b/src/webui/features/tasks/api/cancel-task.ts
@@ -0,0 +1,29 @@
+import {useMutation} from '@tanstack/react-query'
+
+import type {MutationConfig} from '../../../lib/react-query'
+
+import {
+  type TaskCancelRequest,
+  type TaskCancelResponse,
+  TaskEvents,
+} from '../../../../shared/transport/events/task-events'
+import {useTransportStore} from '../../../stores/transport-store'
+
+export const cancelTask = async (payload: TaskCancelRequest): Promise<TaskCancelResponse> => {
+  const {apiClient} = useTransportStore.getState()
+  if (!apiClient) throw new Error('Not connected')
+
+  const response = await apiClient.request<TaskCancelResponse, TaskCancelRequest>(TaskEvents.CANCEL, payload)
+  if (!response.success) throw new Error(response.error ?? 'Cancel failed')
+  return response
+}
+
+type UseCancelTaskOptions = {
+  mutationConfig?: MutationConfig<typeof cancelTask>
+}
+
+export const useCancelTask = ({mutationConfig}: UseCancelTaskOptions = {}) =>
+  useMutation({
+    ...mutationConfig,
+    mutationFn: cancelTask,
+  })
diff --git a/src/webui/features/tasks/components/task-detail-header.tsx b/src/webui/features/tasks/components/task-detail-header.tsx
index 293118684..360b74a69 100644
--- a/src/webui/features/tasks/components/task-detail-header.tsx
+++ b/src/webui/features/tasks/components/task-detail-header.tsx
@@ -1,6 +1,7 @@
 import {Button} from '@campfirein/byterover-packages/components/button'
 import {Tooltip, TooltipContent, TooltipTrigger} from '@campfirein/byterover-packages/components/tooltip'
 import {cn} from '@campfirein/byterover-packages/lib/utils'
+import {CircleStop, LoaderCircle} from 'lucide-react'
 import {toast} from 'sonner'
 
 import type {StoredTask} from '../types/stored-task'
@@ -18,8 +19,16 @@ const STATUS_VERB: Record<StoredTask['status'], string> = {
   started: 'started',
 }
 
-export function DetailHeader({now, task}: {now: number; task: StoredTask}) {
+interface DetailHeaderProps {
+  cancelling: boolean
+  now: number
+  onCancel: (taskId: string) => void
+  task: StoredTask
+}
+
+export function DetailHeader({cancelling, now, onCancel, task}: DetailHeaderProps) {
   const isTerminal = isTerminalStatus(task.status)
+  const isActive = isActiveStatus(task.status)
   const elapsed = elapsedMs(task, now)
   const referenceTime = task.startedAt ?? task.createdAt
   const verb = STATUS_VERB[task.status]
@@ -42,11 +51,22 @@ export function DetailHeader({now, task}: {now: number; task: StoredTask}) {
           {verb} {formatRelative(referenceTime, now)} ago
         </span>
         <Separator />
-        <span
-          className={cn('mono tabular-nums', isActiveStatus(task.status) ? 'text-blue-400' : 'text-muted-foreground')}
-        >
+        <span className={cn('mono tabular-nums', isActive ? 'text-blue-400' : 'text-muted-foreground')}>
           {elapsedLabel} {formatDuration(elapsed)}
         </span>
+        {isActive && (
+          <Button
+            aria-label="Cancel task"
+            className="ml-1 h-6 gap-1 border-red-500/40 px-2 text-red-400 hover:border-red-500/60 hover:bg-red-500/10 hover:text-red-300"
+            disabled={cancelling}
+            onClick={() => onCancel(task.taskId)}
+            size="xs"
+            variant="outline"
+          >
+            {cancelling ? <LoaderCircle className="size-3 animate-spin" /> : <CircleStop className="size-3" />}
+            {cancelling ? 'Cancelling…' : 'Cancel'}
+          </Button>
+        )}
       </div>
     </header>
   )
diff --git a/src/webui/features/tasks/components/task-detail-view.tsx b/src/webui/features/tasks/components/task-detail-view.tsx
index 0a07bb1ba..9f21f07b9 100644
--- a/src/webui/features/tasks/components/task-detail-view.tsx
+++ b/src/webui/features/tasks/components/task-detail-view.tsx
@@ -15,6 +15,8 @@ import {DetailHeader} from './task-detail-header'
 import {ErrorSection, InputSection, LiveStreamSection, NotFound, ResultSection} from './task-detail-sections'
 
 interface TaskDetailViewProps {
+  cancelling: boolean
+  onCancel: (taskId: string) => void
   taskId: string
 }
 
@@ -26,7 +28,7 @@ function hasRichDetail(task: StoredTask | undefined): boolean {
 }
 
 // eslint-disable-next-line complexity
-export function TaskDetailView({taskId}: TaskDetailViewProps) {
+export function TaskDetailView({cancelling, onCancel, taskId}: TaskDetailViewProps) {
   const storeTask = useTaskById(taskId)
   const isLiveInStore = storeTask !== undefined && isActiveStatus(storeTask.status)
   const needsFetch = !hasRichDetail(storeTask) && !isLiveInStore
@@ -80,7 +82,7 @@ export function TaskDetailView({taskId}: TaskDetailViewProps) {
 
   return (
     <div className="flex h-full min-h-0 flex-col">
-      <DetailHeader now={now} task={task} />
+      <DetailHeader cancelling={cancelling} now={now} onCancel={onCancel} task={task} />
       <div className="border-border/50 border-t" />
       <div className="flex min-h-0 flex-1 flex-col gap-7 overflow-y-auto px-6 py-5" onScroll={onScroll} ref={scrollRef}>
         <TourTaskBanner task={task} />
diff --git a/src/webui/features/tasks/components/task-list-table.tsx b/src/webui/features/tasks/components/task-list-table.tsx
index e1ea597d7..92991c0b6 100644
--- a/src/webui/features/tasks/components/task-list-table.tsx
+++ b/src/webui/features/tasks/components/task-list-table.tsx
@@ -10,7 +10,7 @@ import {
 } from '@campfirein/byterover-packages/components/table'
 import {Tooltip, TooltipContent, TooltipTrigger} from '@campfirein/byterover-packages/components/tooltip'
 import {cn} from '@campfirein/byterover-packages/lib/utils'
-import {Trash2} from 'lucide-react'
+import {CircleStop, LoaderCircle, Trash2} from 'lucide-react'
 
 import type {StatusFilter} from '../stores/task-store'
 import type {StoredTask} from '../types/stored-task'
@@ -19,6 +19,7 @@ import {getCurrentActivity} from '../utils/current-activity'
 import {formatProviderModel} from '../utils/format-provider-model'
 import {formatDuration, formatRelative, formatTimeOfDay, shortTaskId} from '../utils/format-time'
 import {isInterrupted} from '../utils/is-interrupted'
+import {rowActionKind} from '../utils/row-action-kind'
 import {displayTaskType, isTerminalStatus} from '../utils/task-status'
 import {StatusPill} from './status-pill'
 import {NoMatchState} from './task-list-empty'
@@ -46,8 +47,10 @@ function durationOf(task: StoredTask, now: number): string {
 
 interface TaskTableProps {
   allSelected: boolean
+  cancellingIds: Set<string>
   filtered: StoredTask[]
   now: number
+  onCancel: (taskId: string) => void
   onClearSearch: () => void
   onDelete: (taskId: string) => void
   onRowClick: (taskId: string) => void
@@ -61,8 +64,10 @@ interface TaskTableProps {
 
 export function TaskTable({
   allSelected,
+  cancellingIds,
   filtered,
   now,
+  onCancel,
   onClearSearch,
   onDelete,
   onRowClick,
@@ -100,9 +105,11 @@ export function TaskTable({
         ) : (
           filtered.map((task) => (
             <TaskRow
+              cancelling={cancellingIds.has(task.taskId)}
               isSelected={selectedIds.has(task.taskId)}
               key={task.taskId}
               now={now}
+              onCancel={onCancel}
               onDelete={onDelete}
               onRowClick={onRowClick}
               onToggleSelect={onToggleSelect}
@@ -117,16 +124,20 @@ export function TaskTable({
 }
 
 function TaskRow({
+  cancelling,
   isSelected,
   now,
+  onCancel,
   onDelete,
   onRowClick,
   onToggleSelect,
   providerNames,
   task,
 }: {
+  cancelling: boolean
   isSelected: boolean
   now: number
+  onCancel: (taskId: string) => void
   onDelete: (taskId: string) => void
   onRowClick: (taskId: string) => void
   onToggleSelect: (taskId: string) => void
@@ -137,6 +148,7 @@ function TaskRow({
   const isRunning = !terminal
   const interrupted = isInterrupted(task)
   const activity = getCurrentActivity(task)
+  const actionKind = rowActionKind(task.status)
 
   const row = (
     <TableRow
@@ -198,7 +210,11 @@ function TaskRow({
         {durationOf(task, now)}
       </TableCell>
       <TableCell className="text-center" onClick={(event) => event.stopPropagation()}>
-        {terminal && <RowAction onClick={() => onDelete(task.taskId)} />}
+        {actionKind === 'delete' ? (
+          <DeleteRowAction onClick={() => onDelete(task.taskId)} />
+        ) : (
+          <CancelRowAction cancelling={cancelling} onClick={() => onCancel(task.taskId)} />
+        )}
       </TableCell>
     </TableRow>
   )
@@ -231,7 +247,7 @@ function ProviderChip({model, provider, providerName}: {model?: string; provider
   )
 }
 
-function RowAction({onClick}: {onClick: () => void}) {
+function DeleteRowAction({onClick}: {onClick: () => void}) {
   return (
     <Button aria-label="Delete" onClick={onClick} size="icon-xs" title="Delete" variant="ghost">
       <Trash2 className="size-3.5" />
@@ -239,6 +255,21 @@ function RowAction({onClick}: {onClick: () => void}) {
   )
 }
 
+function CancelRowAction({cancelling, onClick}: {cancelling: boolean; onClick: () => void}) {
+  return (
+    <Button
+      aria-label="Cancel task"
+      disabled={cancelling}
+      onClick={onClick}
+      size="icon-xs"
+      title={cancelling ? 'Cancelling…' : 'Cancel task'}
+      variant="ghost"
+    >
+      {cancelling ? <LoaderCircle className="size-3.5 animate-spin" /> : <CircleStop className="size-3.5" />}
+    </Button>
+  )
+}
+
 function Checkbox({checked, onChange}: {checked: boolean; onChange: () => void}) {
   return (
     <input
diff --git a/src/webui/features/tasks/components/task-list-view.tsx b/src/webui/features/tasks/components/task-list-view.tsx
index e8e2685ad..99434d8a8 100644
--- a/src/webui/features/tasks/components/task-list-view.tsx
+++ b/src/webui/features/tasks/components/task-list-view.tsx
@@ -10,6 +10,7 @@ import {useTransportStore} from '../../../stores/transport-store'
 import {CURATE_EXAMPLE, QUERY_EXAMPLE, TOUR_STEP_LABEL} from '../../onboarding/lib/tour-examples'
 import {useOnboardingStore} from '../../onboarding/stores/onboarding-store'
 import {useGetProviders} from '../../provider/api/get-providers'
+import {useCancelTask} from '../api/cancel-task'
 import {useClearCompleted} from '../api/clear-completed'
 import {useDeleteBulkTasks} from '../api/delete-bulk-tasks'
 import {useDeleteTask} from '../api/delete-task'
@@ -133,8 +134,10 @@ export function TaskListView() {
   const deleteMutation = useDeleteTask()
   const deleteBulkMutation = useDeleteBulkTasks()
   const clearCompletedMutation = useClearCompleted()
+  const cancelMutation = useCancelTask()
 
   const [selectedIds, setSelectedIds] = useState<Set<string>>(new Set())
+  const [cancellingIds, setCancellingIds] = useState<Set<string>>(new Set())
   const [composer, setComposer] = useState<{
     initialContent?: string
     initialType?: ComposerType
@@ -239,6 +242,33 @@ export function TaskListView() {
     )
   }
 
+  const handleCancel = (taskId: string) => {
+    setCancellingIds((prev) => {
+      const next = new Set(prev)
+      next.add(taskId)
+      return next
+    })
+    const clear = () => {
+      setCancellingIds((prev) => {
+        if (!prev.has(taskId)) return prev
+        const next = new Set(prev)
+        next.delete(taskId)
+        return next
+      })
+    }
+
+    cancelMutation.mutate(
+      {taskId},
+      {
+        onError(err) {
+          toast.error(err.message)
+          clear()
+        },
+        onSuccess: clear,
+      },
+    )
+  }
+
   const deleteSelected = () => {
     const eligibleIds = [...selectedIds].filter((id) => {
       const task = taskMap.get(id)
@@ -357,8 +387,10 @@ export function TaskListView() {
       ) : (
         <TaskTable
           allSelected={allFilteredSelected}
+          cancellingIds={cancellingIds}
           filtered={filtered}
           now={now}
+          onCancel={handleCancel}
           onClearSearch={() => setSearchQuery('')}
           onDelete={handleDelete}
           onRowClick={openTask}
@@ -398,7 +430,13 @@ export function TaskListView() {
           className="data-[side=right]:w-full data-[side=right]:max-w-3xl p-0 shadow-[inset_1px_0_0_rgba(96,165,250,0.18)]"
           side="right"
         >
-          {selectedTaskId && <TaskDetailView taskId={selectedTaskId} />}
+          {selectedTaskId && (
+            <TaskDetailView
+              cancelling={cancellingIds.has(selectedTaskId)}
+              onCancel={handleCancel}
+              taskId={selectedTaskId}
+            />
+          )}
         </SheetContent>
       </Sheet>
 
diff --git a/src/webui/features/tasks/utils/row-action-kind.ts b/src/webui/features/tasks/utils/row-action-kind.ts
new file mode 100644
index 000000000..2b0d64228
--- /dev/null
+++ b/src/webui/features/tasks/utils/row-action-kind.ts
@@ -0,0 +1,9 @@
+import type {TaskListItemStatus} from '../../../../shared/transport/events/task-events'
+
+import {isTerminalStatus} from './task-status'
+
+export type RowActionKind = 'cancel' | 'delete'
+
+export function rowActionKind(status: TaskListItemStatus): RowActionKind {
+  return isTerminalStatus(status) ? 'delete' : 'cancel'
+}
diff --git a/test/unit/webui/features/tasks/api/cancel-task.test.ts b/test/unit/webui/features/tasks/api/cancel-task.test.ts
new file mode 100644
index 000000000..4260c86fb
--- /dev/null
+++ b/test/unit/webui/features/tasks/api/cancel-task.test.ts
@@ -0,0 +1,69 @@
+import {expect} from 'chai'
+import {createSandbox, type SinonSandbox, type SinonStub} from 'sinon'
+
+import type {BrvApiClient} from '../../../../../../src/webui/lib/api-client.js'
+
+import {TaskEvents} from '../../../../../../src/shared/transport/events/task-events.js'
+import {cancelTask} from '../../../../../../src/webui/features/tasks/api/cancel-task.js'
+import {useTransportStore} from '../../../../../../src/webui/stores/transport-store.js'
+
+describe('cancelTask', () => {
+  let sandbox: SinonSandbox
+  let request: SinonStub
+
+  beforeEach(() => {
+    sandbox = createSandbox()
+    request = sandbox.stub()
+    useTransportStore.setState({
+      apiClient: {on: sandbox.stub(), request} as unknown as BrvApiClient,
+    })
+  })
+
+  afterEach(() => {
+    sandbox.restore()
+    useTransportStore.setState({apiClient: null})
+  })
+
+  it('emits task:cancel with the taskId payload', async () => {
+    request.resolves({success: true})
+    await cancelTask({taskId: 'tsk-1'})
+    expect(request.firstCall.args[0]).to.equal(TaskEvents.CANCEL)
+    expect(request.firstCall.args[1]).to.deep.equal({taskId: 'tsk-1'})
+  })
+
+  it('resolves with the daemon response on success', async () => {
+    request.resolves({success: true})
+    const result = await cancelTask({taskId: 'tsk-1'})
+    expect(result).to.deep.equal({success: true})
+  })
+
+  it('throws when the daemon returns success: false', async () => {
+    request.resolves({error: 'Task not found', success: false})
+    try {
+      await cancelTask({taskId: 'tsk-1'})
+      expect.fail('expected to throw')
+    } catch (error) {
+      expect((error as Error).message).to.equal('Task not found')
+    }
+  })
+
+  it('falls back to "Cancel failed" when success: false has no error string', async () => {
+    request.resolves({success: false})
+    try {
+      await cancelTask({taskId: 'tsk-1'})
+      expect.fail('expected to throw')
+    } catch (error) {
+      expect((error as Error).message).to.equal('Cancel failed')
+    }
+  })
+
+  it('throws when not connected to the daemon', async () => {
+    useTransportStore.setState({apiClient: null})
+    try {
+      await cancelTask({taskId: 'tsk-1'})
+      expect.fail('expected to throw')
+    } catch (error) {
+      expect((error as Error).message).to.equal('Not connected')
+    }
+  })
+})
diff --git a/test/unit/webui/features/tasks/utils/row-action-kind.test.ts b/test/unit/webui/features/tasks/utils/row-action-kind.test.ts
new file mode 100644
index 000000000..62624e612
--- /dev/null
+++ b/test/unit/webui/features/tasks/utils/row-action-kind.test.ts
@@ -0,0 +1,25 @@
+import {expect} from 'chai'
+
+import {rowActionKind} from '../../../../../../src/webui/features/tasks/utils/row-action-kind.js'
+
+describe('rowActionKind', () => {
+  it('returns "cancel" for created tasks (running)', () => {
+    expect(rowActionKind('created')).to.equal('cancel')
+  })
+
+  it('returns "cancel" for started tasks (running)', () => {
+    expect(rowActionKind('started')).to.equal('cancel')
+  })
+
+  it('returns "delete" for completed tasks (terminal)', () => {
+    expect(rowActionKind('completed')).to.equal('delete')
+  })
+
+  it('returns "delete" for error tasks (terminal)', () => {
+    expect(rowActionKind('error')).to.equal('delete')
+  })
+
+  it('returns "delete" for cancelled tasks (terminal)', () => {
+    expect(rowActionKind('cancelled')).to.equal('delete')
+  })
+})