diff --git a/k8s/README.md b/k8s/README.md
index b67915f9..fc33f6e0 100644
--- a/k8s/README.md
+++ b/k8s/README.md
@@ -186,3 +186,17 @@ Advanced configuration options.
 | Variable | Description | Scope Configuration Property |
 |----------|-------------|------------------------------|
 | **K8S_MODIFIERS** | JSON string with dynamic modifications to Kubernetes objects | `object_modifiers` |
+
+### ServiceAccounts managed outside the scope
+
+To run pods with an existing ServiceAccount (for example IRSA managed by
+OpenTofu), set the scope capability `service_account_name`. Leave it empty to
+preserve current behavior. Account-level provider defaults are not consulted
+for this opt-in, so other scopes keep their existing identity. Keep managed IAM
+disabled; configuring both ownership modes is rejected.
+
+The ServiceAccount must already exist in the scope's Kubernetes namespace and
+carry the desired IAM role annotation. The deployment builder only selects it
+through `spec.template.spec.serviceAccountName`; the scope does not create or
+delete the external ServiceAccount or its IAM role. Existing managed-IAM naming
+and unconfigured defaults remain unchanged.
diff --git a/k8s/deployment/build_context b/k8s/deployment/build_context
index c0340487..d0a0756f 100755
--- a/k8s/deployment/build_context
+++ b/k8s/deployment/build_context
@@ -199,9 +199,24 @@ fi
 
 IAM_ENABLED=$(echo "$IAM" | jq -r '.ENABLED // false')
 
-SERVICE_ACCOUNT_NAME=""
+# Externally managed ServiceAccounts (for example, IRSA declared in IaC) are
+# selected for the pod without enabling the scope's role/SA lifecycle manager.
+# Explicit scope opt-in: do not start using inherited account-level defaults
+# that older deployments previously ignored.
+EXTERNAL_SERVICE_ACCOUNT_NAME=$(echo "$CONTEXT" | jq -r '.scope.capabilities.service_account_name // empty')
 
-if [[ "$IAM_ENABLED" == "true" ]]; then
+SERVICE_ACCOUNT_NAME=""
+if [[ -n "$EXTERNAL_SERVICE_ACCOUNT_NAME" ]]; then
+  if [[ "$IAM_ENABLED" == "true" ]]; then
+    log error "Configure either an external service_account_name or managed IAM, not both"
+    exit 1
+  fi
+  if [[ ${#EXTERNAL_SERVICE_ACCOUNT_NAME} -gt 253 || ! "$EXTERNAL_SERVICE_ACCOUNT_NAME" =~ ^[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*$ ]]; then
+    log error "Invalid external service_account_name: expected a Kubernetes DNS subdomain name"
+    exit 1
+  fi
+  SERVICE_ACCOUNT_NAME="$EXTERNAL_SERVICE_ACCOUNT_NAME"
+elif [[ "$IAM_ENABLED" == "true" ]]; then
   SERVICE_ACCOUNT_NAME=$(echo "$IAM" | jq -r .PREFIX)-"$SCOPE_ID"
 fi
 
diff --git a/k8s/deployment/tests/build_context.bats b/k8s/deployment/tests/build_context.bats
index 72f95cc6..c8aa2a11 100644
--- a/k8s/deployment/tests/build_context.bats
+++ b/k8s/deployment/tests/build_context.bats
@@ -1302,3 +1302,68 @@ EOF
 
   assert_equal "$(echo "$CONTEXT" | jq -r '.main_traffic_manager_port')" "10080"
 }
+
+# External ServiceAccounts are selected by the real context builder, while IAM
+# role creation/deletion stays disabled for resources owned by IaC.
+@test "external service account: uses the explicitly selected scope account" {
+  setup_full_build_context
+  export IAM='{"ENABLED":false}'
+  CONTEXT=$(echo "$CONTEXT" | jq '.scope.capabilities.service_account_name = "ui-plugins-stage"')
+
+  source "$SCRIPT"
+
+  assert_equal "$(echo "$CONTEXT" | jq -r .service_account_name)" "ui-plugins-stage"
+  assert_equal "$IAM_ENABLED" "false"
+}
+
+@test "external service account: ignores inherited account defaults without scope opt-in" {
+  setup_full_build_context
+  export IAM='{"ENABLED":false}'
+  CONTEXT=$(echo "$CONTEXT" | jq '.providers["container-orchestration"].security.service_account_name = "base-sa"')
+
+  source "$SCRIPT"
+
+  assert_equal "$(echo "$CONTEXT" | jq -r .service_account_name)" ""
+}
+
+@test "external service account: keeps managed IAM name when no external name is configured" {
+  setup_full_build_context
+  export IAM='{"ENABLED":true,"PREFIX":"managed"}'
+
+  source "$SCRIPT"
+
+  assert_equal "$(echo "$CONTEXT" | jq -r .service_account_name)" "managed-test-scope-123"
+}
+
+@test "external service account: leaves the pod default when neither mode is configured" {
+  setup_full_build_context
+  export IAM='{"ENABLED":false}'
+
+  source "$SCRIPT"
+
+  assert_equal "$(echo "$CONTEXT" | jq -r .service_account_name)" ""
+}
+
+@test "external service account: rejects conflicting lifecycle ownership" {
+  setup_full_build_context
+  export IAM='{"ENABLED":true,"PREFIX":"managed"}'
+  CONTEXT=$(echo "$CONTEXT" | jq '.scope.capabilities.service_account_name = "external-sa"')
+  export CONTEXT
+
+  run bash -c 'source "$SCRIPT"'
+
+  [ "$status" -ne 0 ]
+  assert_contains "$output" "either an external service_account_name or managed IAM"
+}
+
+@test "external service account: rejects names that could inject YAML" {
+  setup_full_build_context
+  export IAM='{"ENABLED":false}'
+  CONTEXT=$(echo "$CONTEXT" | jq '.scope.capabilities.service_account_name = "bad\nname"')
+  export CONTEXT
+
+  run bash -c 'source "$SCRIPT"'
+
+  [ "$status" -ne 0 ]
+  assert_contains "$output" "Invalid external service_account_name"
+}
diff --git a/k8s/specs/service-spec.json.tpl b/k8s/specs/service-spec.json.tpl
index 60763b89..516338c2 100644
--- a/k8s/specs/service-spec.json.tpl
+++ b/k8s/specs/service-spec.json.tpl
@@ -61,6 +61,16 @@
                   }
                },
                "elements":[
+                  {
+                     "type":"Category",
+                     "label":"ServiceAccount",
+                     "elements":[
+                        {
+                           "type":"Control",
+                           "scope":"#/properties/service_account_name"
+                        }
+                     ]
+                  },
                   {
                      "type":"Category",
                      "label":"Resources",
@@ -341,6 +351,14 @@
             "export":false,
             "default":"docker-image"
          },
+         "service_account_name": {
+            "type": "string",
+            "title": "Existing ServiceAccount",
+            "default": "",
+            "maxLength": 253,
+            "pattern": "^$|^[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*$",
+            "description": "Use an existing Kubernetes ServiceAccount managed outside this scope. Leave empty for the default. Requires managed IAM to remain disabled."
+         },
          "ram_memory":{
             "type":"integer",
             "oneOf":[