In 1987, the head of the Bureau of Diplomatic Security was elevated to the rank of Assistant Secretary and President Reagan named Lamb as the first Assistant Secretary of State for Diplomatic Security.
President George H. W. Bush then nominated Lamb as United States Ambassador to Cyprus, with Lamb presenting his credentials on November 30, 1990, and serving as Ambassador to Cyprus until October 24, 1993.
He then became Executive Director of the American Philatelic Society in State College, Pennsylvania.
Under his administration, the Society moved its headquarters to an historic, former Match Factory in Bellefonte, Pennsylvania.
Upon his retirement, the Society named the Executive wing of the headquarters complex in his honor.