diff --git a/actions/setup/js/safe_outputs_tools.json b/actions/setup/js/safe_outputs_tools.json
index 9e0d5a3699c..205240c184b 100644
--- a/actions/setup/js/safe_outputs_tools.json
+++ b/actions/setup/js/safe_outputs_tools.json
@@ -1434,7 +1434,7 @@
   },
   {
     "name": "set_issue_field",
-    "description": "Set a single GitHub issue field by name and value. Use field_name for discovery by field label (for example, \"Priority\"), or provide field_node_id to skip discovery. Supports text, number, date (YYYY-MM-DD), and single-select fields (value must match an option name).",
+    "description": "Set a single GitHub issue field by name and value. Use field_name for discovery by field label (for example, \"Priority\"), or provide field_node_id to skip discovery. Supports text, number, date (YYYY-MM-DD), and single-select fields (value must match an option name). Built-in issue properties (\"body\", \"title\") are also supported and are updated via the REST API.",
     "inputSchema": {
       "type": "object",
       "required": ["value"],
diff --git a/actions/setup/js/set_issue_field.cjs b/actions/setup/js/set_issue_field.cjs
index d24119c76b9..3902116937c 100644
--- a/actions/setup/js/set_issue_field.cjs
+++ b/actions/setup/js/set_issue_field.cjs
@@ -17,6 +17,13 @@ const { hasIssueIntentsRuntimeFeature, normalizeIssueIntentMetadata } = require(
 /** @type {string} Safe output type handled by this module */
 const HANDLER_TYPE = "set_issue_field";
 
+/**
+ * Built-in issue fields that are REST properties, not custom project fields.
+ * These are handled via issues.update() instead of the GraphQL setIssueFieldValue mutation.
+ * @type {Set<string>}
+ */
+const BUILTIN_ISSUE_FIELDS = new Set(["body", "title"]);
+
 /**
  * Fetches the node ID of an issue for use in GraphQL mutations.
  * @param {Object} githubClient - Authenticated GitHub client
@@ -265,6 +272,37 @@ async function main(config = {}) {
       };
     }
 
+    const fieldNameLower = fieldName.toLowerCase();
+
+    // Handle built-in issue properties (body, title) via REST API instead of the custom fields GraphQL API.
+    if (fieldName && BUILTIN_ISSUE_FIELDS.has(fieldNameLower)) {
+      try {
+        validateAllowedIssueFieldName(fieldName, allowedIssueFields);
+
+        const { owner, repo } = repoParts;
+        await githubClient.rest.issues.update({
+          owner,
+          repo,
+          issue_number: issueNumber,
+          [fieldNameLower]: value,
+        });
+
+        core.info(`Successfully set builtin issue field ${JSON.stringify(fieldName)} on issue #${issueNumber}`);
+
+        return {
+          success: true,
+          issue_number: issueNumber,
+          field_name: fieldName,
+          value,
+          repo: itemRepo,
+        };
+      } catch (error) {
+        const errorMessage = getErrorMessage(error);
+        core.error(`Failed to set builtin issue field ${JSON.stringify(fieldName)} on issue #${issueNumber}: ${errorMessage}`);
+        return { success: false, error: errorMessage };
+      }
+    }
+
     try {
       const { owner, repo } = repoParts;
       const issueNodeId = await getIssueNodeId(githubClient, owner, repo, issueNumber);
diff --git a/actions/setup/js/set_issue_field.test.cjs b/actions/setup/js/set_issue_field.test.cjs
index 75d1a0c626c..25b6ee2b723 100644
--- a/actions/setup/js/set_issue_field.test.cjs
+++ b/actions/setup/js/set_issue_field.test.cjs
@@ -32,6 +32,7 @@ const mockGithub = {
   rest: {
     issues: {
       get: vi.fn(),
+      update: vi.fn(),
     },
   },
   graphql: mockGraphql,
@@ -79,6 +80,7 @@ describe("set_issue_field (Handler Factory Architecture)", () => {
     vi.clearAllMocks();
 
     mockGithub.rest.issues.get.mockResolvedValue({ data: { node_id: issueNodeId } });
+    mockGithub.rest.issues.update.mockResolvedValue({ data: {} });
     mockGraphql.mockImplementation(query => {
       if (query.includes("issueFields")) {
         return Promise.resolve(mockIssueFieldsQuery);
@@ -451,4 +453,96 @@ describe("set_issue_field (Handler Factory Architecture)", () => {
       delete process.env.GH_AW_RUNTIME_FEATURES;
     }
   });
+
+  it("should update builtin 'body' field via REST API without querying project fields", async () => {
+    const message = {
+      type: "set_issue_field",
+      issue_number: 42,
+      field_name: "body",
+      value: "Updated issue body text",
+    };
+
+    const result = await handler(message, {});
+
+    expect(result.success).toBe(true);
+    expect(result.issue_number).toBe(42);
+    expect(result.field_name).toBe("body");
+    expect(result.value).toBe("Updated issue body text");
+    expect(mockGithub.rest.issues.update).toHaveBeenCalledWith(
+      expect.objectContaining({
+        issue_number: 42,
+        body: "Updated issue body text",
+      })
+    );
+    // Must NOT query GraphQL custom fields
+    expect(mockGraphql).not.toHaveBeenCalledWith(expect.stringContaining("issueFields"), expect.anything());
+    expect(mockGraphql).not.toHaveBeenCalledWith(expect.stringContaining("setIssueFieldValue"), expect.anything());
+  });
+
+  it("should update builtin 'title' field via REST API", async () => {
+    const message = {
+      type: "set_issue_field",
+      issue_number: 42,
+      field_name: "title",
+      value: "New issue title",
+    };
+
+    const result = await handler(message, {});
+
+    expect(result.success).toBe(true);
+    expect(result.issue_number).toBe(42);
+    expect(result.field_name).toBe("title");
+    expect(mockGithub.rest.issues.update).toHaveBeenCalledWith(
+      expect.objectContaining({
+        issue_number: 42,
+        title: "New issue title",
+      })
+    );
+    expect(mockGraphql).not.toHaveBeenCalledWith(expect.stringContaining("issueFields"), expect.anything());
+  });
+
+  it("should handle builtin field name case-insensitively (Body -> body)", async () => {
+    const message = {
+      type: "set_issue_field",
+      issue_number: 42,
+      field_name: "Body",
+      value: "Some body",
+    };
+
+    const result = await handler(message, {});
+
+    expect(result.success).toBe(true);
+    expect(mockGithub.rest.issues.update).toHaveBeenCalledWith(expect.objectContaining({ issue_number: 42, body: "Some body" }));
+  });
+
+  it("should respect allowed-fields restriction for builtin fields", async () => {
+    const { main } = require("./set_issue_field.cjs");
+    const restrictedHandler = await main({ allowed_fields: ["title"] });
+
+    const result = await restrictedHandler({
+      type: "set_issue_field",
+      issue_number: 42,
+      field_name: "body",
+      value: "Blocked body update",
+    });
+
+    expect(result.success).toBe(false);
+    expect(result.error).toContain('"body" is not in the allowed-fields list');
+    expect(mockGithub.rest.issues.update).not.toHaveBeenCalled();
+  });
+
+  it("should allow builtin field when allowed-fields includes wildcard", async () => {
+    const { main } = require("./set_issue_field.cjs");
+    const wildcardHandler = await main({ allowed_fields: ["*"] });
+
+    const result = await wildcardHandler({
+      type: "set_issue_field",
+      issue_number: 42,
+      field_name: "body",
+      value: "Allowed body update",
+    });
+
+    expect(result.success).toBe(true);
+    expect(mockGithub.rest.issues.update).toHaveBeenCalledWith(expect.objectContaining({ issue_number: 42, body: "Allowed body update" }));
+  });
 });
diff --git a/pkg/workflow/js/safe_outputs_tools.json b/pkg/workflow/js/safe_outputs_tools.json
index 9e0d5a3699c..205240c184b 100644
--- a/pkg/workflow/js/safe_outputs_tools.json
+++ b/pkg/workflow/js/safe_outputs_tools.json
@@ -1434,7 +1434,7 @@
   },
   {
     "name": "set_issue_field",
-    "description": "Set a single GitHub issue field by name and value. Use field_name for discovery by field label (for example, \"Priority\"), or provide field_node_id to skip discovery. Supports text, number, date (YYYY-MM-DD), and single-select fields (value must match an option name).",
+    "description": "Set a single GitHub issue field by name and value. Use field_name for discovery by field label (for example, \"Priority\"), or provide field_node_id to skip discovery. Supports text, number, date (YYYY-MM-DD), and single-select fields (value must match an option name). Built-in issue properties (\"body\", \"title\") are also supported and are updated via the REST API.",
     "inputSchema": {
       "type": "object",
       "required": ["value"],