Mitt Romney has hired Richard A. Grenell, a veteran Republican communications strategist who served in the George W. Bush administration, as his national security and foreign policy spokesman, a campaign official said Thursday.

Grenell brings foreign policy chops and more than a decade of political experience to the aggressive but relatively young Romney staff. His is one in a series of hires as the presumptive Republican nominee rapidly expands his small staff as it moves into the general election against President Obama.

During all eight years of President George W. Bush’s tenure, Grenell served as the administration’s director of communications and public diplomacy at the United Nations. He advised four U.S. ambassadors to the United Nations: John D. Negroponte, John C. Danforth, John R. Bolton and Zalmay Khalilzad.

Before his work at the United Nations, Grenell served as a spokesman for New York Governor George Pataki (R) and San Diego Mayor Susan Golding (R), as well as Rep. Dave Camp (R-Mich.), currently chairman of the House Ways and Means Committee, and then-Rep. Mark Sanford (R-S.C.), before Sanford was elected governor.

Since leaving the Bush administration, Grenell has been based in Los Angeles as a partner with Capitol Media Partners.