diff --git a/src/features/team-mode/team-runtime/delete-team-bg-cancel.test.ts b/src/features/team-mode/team-runtime/delete-team-bg-cancel.test.ts
new file mode 100644
index 000000000..d29bd0088
--- /dev/null
+++ b/src/features/team-mode/team-runtime/delete-team-bg-cancel.test.ts
@@ -0,0 +1,84 @@
+/// <reference types="bun-types" />
+
+import { afterEach, describe, expect, mock, test } from "bun:test"
+import { rm } from "node:fs/promises"
+
+import type { BackgroundManager } from "../../background-agent/manager"
+import { createFixture, updateMemberStatuses } from "./shutdown-test-fixtures"
+
+const { deleteTeam } = await import("./delete-team")
+
+describe("deleteTeam cancels only this team's background tasks", () => {
+  const temporaryDirectories: string[] = []
+
+  afterEach(async () => {
+    await Promise.all(temporaryDirectories.splice(0).map(async (directoryPath) => {
+      await rm(directoryPath, { recursive: true, force: true })
+    }))
+  })
+
+  test("uses leadSessionId as the getTasksByParentSession key", async () => {
+    // given
+    const fixture = await createFixture()
+    temporaryDirectories.push(fixture.baseDir)
+    await updateMemberStatuses(fixture.teamRunId, fixture.config, {
+      "member-a": "shutdown_approved",
+      "member-b": "shutdown_approved",
+    })
+
+    const getTasksByParentSessionMock = mock((sessionID: string) => {
+      if (sessionID !== "lead-session") return []
+      return [
+        { id: "team-task-a", sessionID: "session-a", parentMessageID: `team-create:${fixture.teamRunId}:member-a` },
+        { id: "team-task-b", sessionID: "session-b", parentMessageID: `team-create:${fixture.teamRunId}:member-b` },
+      ]
+    })
+    const cancelTaskMock = mock(async () => true)
+    const bgMgr = {
+      getTasksByParentSession: getTasksByParentSessionMock,
+      cancelTask: cancelTaskMock,
+    } as unknown as BackgroundManager
+
+    // when
+    await deleteTeam(fixture.teamRunId, fixture.config, undefined, bgMgr)
+
+    // then
+    expect(getTasksByParentSessionMock).toHaveBeenCalledTimes(1)
+    expect(getTasksByParentSessionMock).toHaveBeenCalledWith("lead-session")
+    expect(cancelTaskMock).toHaveBeenCalledTimes(2)
+    const firstCall = cancelTaskMock.mock.calls[0]
+    const secondCall = cancelTaskMock.mock.calls[1]
+    expect(firstCall?.[0]).toBe("team-task-a")
+    expect(secondCall?.[0]).toBe("team-task-b")
+  })
+
+  test("leaves unrelated sibling tasks on the same lead session alive", async () => {
+    // given
+    const fixture = await createFixture()
+    temporaryDirectories.push(fixture.baseDir)
+    await updateMemberStatuses(fixture.teamRunId, fixture.config, {
+      "member-a": "shutdown_approved",
+      "member-b": "shutdown_approved",
+    })
+
+    const getTasksByParentSessionMock = mock(() => [
+      { id: "team-task-a", sessionID: "session-a", parentMessageID: `team-create:${fixture.teamRunId}:member-a` },
+      { id: "delegate-task-x", sessionID: "session-x", parentMessageID: "delegate-task:plan-refactor" },
+      { id: "background-task-y", sessionID: "session-y", parentMessageID: undefined },
+      { id: "team-task-other", sessionID: "session-other", parentMessageID: "team-create:other-team-id:member-a" },
+    ])
+    const cancelTaskMock = mock(async () => true)
+    const bgMgr = {
+      getTasksByParentSession: getTasksByParentSessionMock,
+      cancelTask: cancelTaskMock,
+    } as unknown as BackgroundManager
+
+    // when
+    await deleteTeam(fixture.teamRunId, fixture.config, undefined, bgMgr)
+
+    // then
+    expect(cancelTaskMock).toHaveBeenCalledTimes(1)
+    const cancelledTaskId = cancelTaskMock.mock.calls[0]?.[0]
+    expect(cancelledTaskId).toBe("team-task-a")
+  })
+})
diff --git a/src/features/team-mode/team-runtime/delete-team.ts b/src/features/team-mode/team-runtime/delete-team.ts
new file mode 100644
index 000000000..385e90a3e
--- /dev/null
+++ b/src/features/team-mode/team-runtime/delete-team.ts
@@ -0,0 +1,134 @@
+import type { TeamModeConfig } from "../../../config/schema/team-mode"
+import { log } from "../../../shared/logger"
+import type { BackgroundManager } from "../../background-agent/manager"
+import type { TmuxSessionManager } from "../../tmux-subagent/manager"
+import { canVisualize, removeTeamLayout } from "../team-layout-tmux/layout"
+import { sweepStaleTeamSessions } from "../team-layout-tmux/sweep-stale-team-sessions"
+import { getRuntimeStateDir, resolveBaseDir } from "../team-registry/paths"
+import { unregisterTeamSessionsByTeam } from "../team-session-registry"
+import { listActiveTeams, loadRuntimeState, saveRuntimeState, transitionRuntimeState } from "../team-state-store/store"
+import type { RuntimeState } from "../types"
+import { DELETABLE_MEMBER_STATUSES, removeWorktrees } from "./shutdown-helpers"
+
+const DELETABLE_TEAM_STATUSES = new Set<RuntimeState["status"]>([
+  "active",
+  "shutdown_requested",
+  "deleting",
+  "deleted",
+])
+
+const FORCE_DELETABLE_TEAM_STATUSES = new Set<RuntimeState["status"]>([
+  ...DELETABLE_TEAM_STATUSES,
+  "creating",
+  "orphaned",
+])
+
+const FORCE_COMPLETABLE_MEMBER_STATUSES = new Set<RuntimeState["members"][number]["status"]>([
+  "pending",
+  "running",
+  "idle",
+])
+
+const FORCE_BYPASS_DELETING_STATUSES = new Set<RuntimeState["status"]>(["creating", "orphaned"])
+
+export async function deleteTeam(
+  teamRunId: string,
+  config: TeamModeConfig,
+  tmuxMgr?: TmuxSessionManager,
+  bgMgr?: BackgroundManager,
+  options?: { force?: boolean },
+): Promise<{ removedWorktrees: string[]; removedLayout: boolean }> {
+  const runtimeState = await loadRuntimeState(teamRunId, config)
+  const nonLeadMembers = runtimeState.members.filter((member) => member.agentType !== "leader")
+
+  if (bgMgr && runtimeState.leadSessionId) {
+    const teamMessageMarkerPrefix = `team-create:${teamRunId}:`
+    const teamTasks = bgMgr.getTasksByParentSession(runtimeState.leadSessionId)
+      .filter((task) => task.teamRunId === teamRunId || task.parentMessageID?.startsWith(teamMessageMarkerPrefix))
+    await Promise.all(teamTasks.map((task) => bgMgr.cancelTask(task.id, {
+      source: "team-mode-delete",
+      reason: `delete team ${teamRunId}`,
+    })))
+  }
+
+  if (options?.force === true) {
+    await transitionRuntimeState(teamRunId, (currentRuntimeState) => ({
+      ...currentRuntimeState,
+      members: currentRuntimeState.members.map((member) => (
+        member.agentType === "leader" || !FORCE_COMPLETABLE_MEMBER_STATUSES.has(member.status)
+          ? member
+          : { ...member, status: "completed" }
+      )),
+    }), config)
+  } else if (nonLeadMembers.some((member) => !DELETABLE_MEMBER_STATUSES.has(member.status))) {
+    throw new Error("members still active")
+  }
+
+  const deletableTeamStatuses = options?.force === true
+    ? FORCE_DELETABLE_TEAM_STATUSES
+    : DELETABLE_TEAM_STATUSES
+  if (!deletableTeamStatuses.has(runtimeState.status)) {
+    throw new Error(`team cannot be deleted from '${runtimeState.status}'`)
+  }
+
+  if (runtimeState.status !== "deleting" && runtimeState.status !== "deleted") {
+    if (options?.force === true && FORCE_BYPASS_DELETING_STATUSES.has(runtimeState.status)) {
+      const currentRuntimeState = await loadRuntimeState(teamRunId, config)
+      if (currentRuntimeState.status !== "deleting" && currentRuntimeState.status !== "deleted") {
+        await saveRuntimeState({ ...currentRuntimeState, status: "deleting" }, config)
+      }
+    } else {
+      await transitionRuntimeState(teamRunId, (currentRuntimeState) => (
+        currentRuntimeState.status === "deleting"
+          ? currentRuntimeState
+          : { ...currentRuntimeState, status: "deleting" }
+      ), config)
+    }
+  }
+
+  const removedLayout = tmuxMgr !== undefined && canVisualize()
+  if (removedLayout) {
+    const memberPaneIds = runtimeState.members
+      .filter((member) => member.agentType !== "leader" && member.tmuxPaneId)
+      .map((member) => member.tmuxPaneId!)
+
+    const cleanupTarget = runtimeState.tmuxLayout
+      ? {
+          ...runtimeState.tmuxLayout,
+          paneIds: memberPaneIds.length > 0 ? memberPaneIds : undefined,
+        }
+      : undefined
+
+    if (options?.force === true) {
+      try {
+        await removeTeamLayout(teamRunId, cleanupTarget, tmuxMgr)
+      } catch (error) {
+        log("team delete layout cleanup failed", {
+          teamRunId,
+          error: error instanceof Error ? error.message : String(error),
+        })
+      }
+    } else {
+      await removeTeamLayout(teamRunId, cleanupTarget, tmuxMgr)
+    }
+  }
+
+  const removedWorktrees = await removeWorktrees(runtimeState.members.map((member) => member.worktreePath))
+
+  if (runtimeState.status !== "deleted") {
+    await transitionRuntimeState(teamRunId, (currentRuntimeState) => (
+      currentRuntimeState.status === "deleted"
+        ? currentRuntimeState
+        : { ...currentRuntimeState, status: "deleted" }
+    ), config)
+  }
+
+  await removeWorktrees([getRuntimeStateDir(resolveBaseDir(config), teamRunId)])
+
+  unregisterTeamSessionsByTeam(teamRunId)
+
+  const activeTeams = await listActiveTeams(config)
+  sweepStaleTeamSessions(new Set(activeTeams.map((team) => team.teamRunId))).catch(() => {})
+
+  return { removedWorktrees, removedLayout }
+}