diff --git a/pkg/apis/serving/k8s_validation.go b/pkg/apis/serving/k8s_validation.go
index 5a8cff484cc9..459eacdc819d 100644
--- a/pkg/apis/serving/k8s_validation.go
+++ b/pkg/apis/serving/k8s_validation.go
@@ -925,6 +925,17 @@ func validateProbe(p *corev1.Probe, port *corev1.ContainerPort, isUserContainer
 	} else if len(handlers) > 1 {
 		errs = errs.Also(apis.ErrMultipleOneOf(handlers...))
 	}
+
+	// Validate TerminationGracePeriodSeconds if set
+	if p.TerminationGracePeriodSeconds != nil {
+		if *p.TerminationGracePeriodSeconds < 0 {
+			errs = errs.Also(&apis.FieldError{
+				Message: "terminationGracePeriodSeconds must be non-negative",
+				Paths:   []string{"terminationGracePeriodSeconds"},
+			})
+		}
+	}
+
 	return errs
 }
 
diff --git a/pkg/apis/serving/v1/revision_defaults.go b/pkg/apis/serving/v1/revision_defaults.go
index f2014724bf45..1419a6b93986 100644
--- a/pkg/apis/serving/v1/revision_defaults.go
+++ b/pkg/apis/serving/v1/revision_defaults.go
@@ -138,6 +138,7 @@ func (rs *RevisionSpec) applyDefault(ctx context.Context, container *corev1.Cont
 	}
 	rs.applyReadinessProbeDefaults(container)
 	rs.applyGRPCProbeDefaults(container)
+	rs.applyLivenessProbeDefaults(container)
 
 	if rs.PodSpec.EnableServiceLinks == nil && apis.IsInCreate(ctx) {
 		rs.PodSpec.EnableServiceLinks = cfg.Defaults.EnableServiceLinks
@@ -203,6 +204,14 @@ func (*RevisionSpec) applyGRPCProbeDefaults(container *corev1.Container) {
 	}
 }
 
+// applyLivenessProbeDefaults applies default TerminationGracePeriodSeconds to liveness probe
+func (*RevisionSpec) applyLivenessProbeDefaults(container *corev1.Container) {
+	if container.LivenessProbe != nil && container.LivenessProbe.TerminationGracePeriodSeconds == nil {
+		// Default to 1 second for liveness probe termination grace period
+		container.LivenessProbe.TerminationGracePeriodSeconds = ptr.Int64(1)
+	}
+}
+
 // Upgrade SecurityContext for this container and the Pod definition to use settings
 // for the `restricted` profile when the feature flag is enabled.
 // when the feature flag is enabled or AllowRootBounded: