Karlin began her career in government as a career civil servant in the
Office of the Secretary of Defense. She later became the Deputy Assistant Secretary of Defense for Strategy and Force Development during the
Obama administration. In that capacity, she helped develop the 2015
National Security Strategy and the 2014
Quadrennial Defense Review. Upon leaving the Obama administration, Karlin returned to her alma mater, Johns Hopkins University's
School of Advanced International Studies, to first become the deputy director of the Strategic Studies Department and later its Director until leaving academia for government. During her time at Johns Hopkins University, she also served as an associate professor. Simultaneously, Karlin served as a nonresident senior fellow with the Center for Security, Strategy, and Technology at the Brookings Institution In 2018, Karlin was on the National Defense Strategy Commission staff, and a member of the congressionally appointed Syria Study Group.
Biden administration Karlin was on the defense policy team for the Biden-Harris transition. In January 2021, Karlin was appointed to serve as the Principal Deputy Assistant Secretary of Defense for International Security Affairs. The position did not require Senate confirmation, and she began service on January 20, 2021, immediately after President Biden was inaugurated. As the most senior member of the International Security Affairs Office, Karlin became the Acting
Assistant Secretary of Defense for International Security Affairs, leading the department's relations with nearly 150 countries. In April 2021, the
White House announced that President
Joe Biden had nominated Karlin as
Assistant Secretary of Defense for Strategy, Plans, & Capabilities. Karlin received
Senate confirmation on August 9. In this role Karlin led development of the 2022 National Defense Strategy, Nuclear Posture Review, and Missile Defense Review—the first integrated strategy review in Department of Defense history. In this capacity, she also was responsible for advising the Secretary of Defense and others on the forces, plans, posture, emerging capabilities, and security cooperation activities necessary to implement the National Defense Strategy. As part of this, she manages policy and strategy for the Defense Security Cooperation Agency (DSCA). In addition to her role in writing and implementing the 2022 National Defense Strategy, Karlin guided the AUKUS agreement between the US, UK, and Australia, which, according to a speech by President Biden, is meant to help in "developing Australia’s conventionally armed nuclear-powered submarine capacity" Karlin also helped form a new emerging capabilities policy office. On 11 December 2023, Karlin announced that she would be stepping down from her position as Acting Deputy Under Secretary of Defense for Policy and Assistant Secretary of Defense for Strategy, Plans, and Capabilities, to take up a position in
academia. On July 8, 2024, the
Brookings Institution announced that Karlin had been appointed a visiting fellow. ==Publications==