diff --git a/CLAUDE.md b/CLAUDE.md
index 26c7c3fb..3a39136b 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -135,7 +135,7 @@ This naming avoids AWS-specific "profile" terminology and uses a clear verb for
 
 Environment variables:
 - `LOCALSTACK_AUTH_TOKEN` - Auth token (skips browser login if set)
-- `LSTK_STARTUP_TIMEOUT` - Startup readiness deadline for `lstk start` (Go duration). Zero/unset uses the per-mode default resolved in `resolveStartupTimeout` (`internal/container/start.go`): 20s interactive (deadline only shows a recoverable keep-waiting/stop prompt, re-armed by "keep waiting"), 60s non-interactive (fatal; the container is left running for inspection). Container exits are detected separately — and instantly, with the exit code — via the exit wait `runtime.Runtime.Start` registers between create and start.
+- `LSTK_STARTUP_TIMEOUT` - Startup readiness deadline for `lstk start` (Go duration). Zero/unset uses the per-mode default resolved in `resolveStartupTimeout` (`internal/container/start.go`): 20s interactive (deadline only shows a recoverable keep-waiting/stop prompt, re-armed by "keep waiting"), 60s non-interactive (fatal; the container is left running for inspection). Container exits are detected separately — and instantly, with the exit code — via the exit wait `runtime.Runtime.Start` registers between create and start. `lstk start --timeout <duration>` (also on the bare root) overrides this for a single run; the flag wins over the env var when explicitly set, and `--timeout 0` falls back to the per-mode default (`addTimeoutFlag`/`applyTimeoutFlag` in `cmd/root.go`). `restart` and the snapshot auto-start path do not expose the flag.
 - `LSTK_OTEL=1` - Enables OpenTelemetry trace export (disabled by default); when enabled, standard `OTEL_EXPORTER_OTLP_*` env vars are respected by the SDK. Requires an OTLP-compatible backend to receive and visualize telemetry — for local development, `make otel` starts one (UI at http://localhost:16686).
 - `LSTK_MERGE_STRATEGY` - Default merge strategy for `snapshot load` / `load` (`account-region-merge`, `overwrite`, or `service-merge`) when `--merge` is not passed; an explicit `--merge` always wins. Resolved in `resolveMergeStrategy` (`cmd/snapshot.go`).
 
diff --git a/cmd/root.go b/cmd/root.go
index d056bdd2..07651575 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -83,6 +83,9 @@ func NewRootCmd(cfg *env.Env, tel *telemetry.Client, logger log.Logger) *cobra.C
 			if err != nil {
 				return err
 			}
+			if err := applyTimeoutFlag(cmd, cfg); err != nil {
+				return err
+			}
 			return startEmulator(cmd.Context(), rt, cfg, tel, logger, persist, firstRun, snapshotFlag, noSnapshot, emulatorType)
 		},
 	}
@@ -129,6 +132,7 @@ func NewRootCmd(cfg *env.Env, tel *telemetry.Client, logger log.Logger) *cobra.C
 	root.Flags().Bool("persist", false, "Persist emulator state across restarts")
 	addEmulatorTypeFlag(root)
 	addSnapshotStartFlags(root)
+	addTimeoutFlag(root)
 
 	// Parse lstk's global flags only when they precede the command name: with
 	// interspersing disabled, Cobra consumes leading flags and hands everything
@@ -402,6 +406,30 @@ func resolveEmulatorTypeFlag(cmd *cobra.Command) (config.EmulatorType, error) {
 	return config.ParseEmulatorType(flagVal)
 }
 
+// addTimeoutFlag registers the --timeout flag on a start-capable command. It is
+// a per-run override of LSTK_STARTUP_TIMEOUT / the startup_timeout config; 0
+// (the default) leaves the env/config value in place, which in turn falls back
+// to the per-mode default in resolveStartupTimeout. restart and the snapshot
+// auto-start path deliberately do not expose this flag.
+func addTimeoutFlag(cmd *cobra.Command) {
+	cmd.Flags().Duration("timeout", 0, "Maximum time to wait for the emulator to become ready (overrides LSTK_STARTUP_TIMEOUT; 0 uses the default)")
+}
+
+// applyTimeoutFlag lets --timeout override the env/config-derived
+// cfg.StartupTimeout, but only when the flag was explicitly set, so an unset
+// flag preserves the LSTK_STARTUP_TIMEOUT value.
+func applyTimeoutFlag(cmd *cobra.Command, cfg *env.Env) error {
+	if !cmd.Flags().Changed("timeout") {
+		return nil
+	}
+	timeout, err := cmd.Flags().GetDuration("timeout")
+	if err != nil {
+		return err
+	}
+	cfg.StartupTimeout = timeout
+	return nil
+}
+
 // walkCommandsWithRunE walks the Cobra command tree rooted at cmd, calling wrap
 // on every command that has a RunE so callers can layer cross-cutting behavior
 // (telemetry, JSON gating, tracing) onto it.
diff --git a/cmd/start.go b/cmd/start.go
index 8271eeb1..5f687e0f 100644
--- a/cmd/start.go
+++ b/cmd/start.go
@@ -46,11 +46,15 @@ If a snapshot is configured for the AWS emulator (the snapshot field in [[contai
 			if err != nil {
 				return err
 			}
+			if err := applyTimeoutFlag(c, cfg); err != nil {
+				return err
+			}
 			return startEmulator(c.Context(), rt, cfg, tel, logger, persist, firstRun, snapshotFlag, noSnapshot, emulatorType)
 		},
 	}
 	cmd.Flags().Bool("persist", false, "Persist emulator state across restarts")
 	addEmulatorTypeFlag(cmd)
 	addSnapshotStartFlags(cmd)
+	addTimeoutFlag(cmd)
 	return cmd
 }
diff --git a/test/integration/main_test.go b/test/integration/main_test.go
index 46ec3297..c356d1e2 100644
--- a/test/integration/main_test.go
+++ b/test/integration/main_test.go
@@ -234,6 +234,43 @@ func startExternalContainer(t *testing.T, ctx context.Context, imgName, name, ho
 	})
 }
 
+// commitNeverHealthyImage builds a local-only image whose default command stays
+// running (sleep infinity) but never serves /_localstack/health. Starting it via
+// lstk exercises the failure path where the emulator comes up but never reports
+// healthy. The tag must stay pinned (non-latest): a pinned locally-present image
+// skips both the pull and the license checks, while a "latest" tag is validated
+// post-pull via GetImageVersion, which fails on this image (no
+// LOCALSTACK_BUILD_VERSION) before the health wait is ever reached. Returns the
+// image reference; the image and its source container are removed on test cleanup.
+func commitNeverHealthyImage(t *testing.T, ctx context.Context) string {
+	t.Helper()
+
+	reader, err := dockerClient.ImagePull(ctx, testImage, client.ImagePullOptions{})
+	require.NoError(t, err, "failed to pull test image")
+	_, _ = io.Copy(io.Discard, reader)
+	_ = reader.Close()
+
+	resp, err := dockerClient.ContainerCreate(ctx, client.ContainerCreateOptions{
+		Config: &container.Config{Image: testImage},
+		Name:   "lstk-never-healthy-src",
+	})
+	require.NoError(t, err, "failed to create source container")
+	t.Cleanup(func() {
+		_, _ = dockerClient.ContainerRemove(context.Background(), resp.ID, client.ContainerRemoveOptions{Force: true})
+	})
+
+	const imageRef = "lstk-never-healthy:test"
+	_, err = dockerClient.ContainerCommit(ctx, resp.ID, client.ContainerCommitOptions{
+		Reference: imageRef,
+		Changes:   []string{`CMD ["sleep", "infinity"]`},
+	})
+	require.NoError(t, err, "failed to commit never-healthy image")
+	t.Cleanup(func() {
+		_, _ = dockerClient.ImageRemove(context.Background(), imageRef, client.ImageRemoveOptions{Force: true})
+	})
+	return imageRef
+}
+
 func startTestSnowflakeContainer(t *testing.T, ctx context.Context) {
 	t.Helper()
 	startNamedTestContainer(t, ctx, snowflakeContainerName, "snowflake")
diff --git a/test/integration/start_test.go b/test/integration/start_test.go
index 95987a67..d38b2395 100644
--- a/test/integration/start_test.go
+++ b/test/integration/start_test.go
@@ -1075,6 +1075,46 @@ image = "lstk-nonexistent-custom-image"
 	assert.Contains(t, combined, "Failed to pull lstk-nonexistent-custom-image:latest")
 }
 
+// TestStartTimesOutWhenEmulatorNeverBecomesHealthy verifies that --timeout bounds
+// the health-check wait (PRO-357): a container that stays running but never serves
+// /_localstack/health must fail fast with a clear error and a non-zero exit,
+// instead of hanging indefinitely.
+func TestStartTimesOutWhenEmulatorNeverBecomesHealthy(t *testing.T) {
+	requireDocker(t)
+	cleanup()
+	t.Cleanup(cleanup)
+
+	ctx := testContext(t)
+	imageRef := commitNeverHealthyImage(t, ctx)
+	imageName, imageTag, ok := strings.Cut(imageRef, ":")
+	require.True(t, ok, "never-healthy image reference must carry a pinned tag")
+
+	// A non-interactive startup timeout deliberately leaves the container running
+	// for inspection, and the pinned tag names it "localstack-aws-<tag>" — a name
+	// the shared cleanup() (which only removes "localstack-aws") never touches.
+	// Remove it explicitly, or it keeps holding port 4566 and breaks every later
+	// test that starts an emulator. Registered after commitNeverHealthyImage's
+	// cleanups so it runs before them (LIFO): the container goes first, then its image.
+	t.Cleanup(func() {
+		_, _ = dockerClient.ContainerRemove(context.Background(), "localstack-aws-"+imageTag, client.ContainerRemoveOptions{Force: true})
+	})
+
+	home := t.TempDir()
+	configFile := filepath.Join(home, "config.toml")
+	require.NoError(t, os.WriteFile(configFile,
+		[]byte(fmt.Sprintf("[[containers]]\ntype = \"aws\"\nport = \"4566\"\nimage = %q\ntag = %q\n", imageName, imageTag)), 0644))
+
+	// A pinned tag already present locally skips both the pull and the license
+	// checks (see commitNeverHealthyImage), so a dummy token is enough to reach
+	// the health wait.
+	e := append(testEnvWithHome(home, ""), string(env.AuthToken)+"=fake-token")
+	stdout, stderr, err := runLstk(t, ctx, "", e, "--config", configFile, "--non-interactive", "start", "--timeout", "3s")
+
+	require.Error(t, err, "expected start to fail when the emulator never becomes healthy")
+	requireExitCode(t, 1, err)
+	assert.Contains(t, stdout+stderr, "LocalStack did not become ready within 3s")
+}
+
 // TestStartFallsBackToLocalImageWhenPullFails verifies the offline degradation
 // path for image pulls: when the configured image cannot be pulled (registry
 // unreachable, or the image was never published) but is already present locally,