Countryman served for 35 years as a member of the Foreign Service until January 2017, achieving the rank of minister-counselor, and served as acting undersecretary for arms control and international security, a position to which he was appointed Oct. 9, 2016. Appointed by President Obama in 2011, he simultaneously served as assistant secretary for international security and nonproliferation, a position he had held since September 2011. As acting undersecretary, he advised the Secretary of State on arms control, nonproliferation, disarmament and political-military affairs.
In January, 2017, while traveling to an international arms control conference, he was informed he had been relieved of all duties by President Trump.
In the White House he was at the National Security Council he was responsible of for the area ranging from Morocco to Syria and was Ambassador Dennis Ross’s liaison with the White House.
Countryman was elected to join the board of the Arms Control Association in June 2017. Since leaving government and joining the Association’s board, he has spoken on the Association’s concerns in interviews in The Guardian, Voice of America, CNN, and NBC News and has written for The Washington Post and other publications.