Stimson served as the Deputy Assistant Secretary of Defense for Detainee Affairs from 2005 until his resignation on February 2, 2007, following a controversy about his statements on legal representation for prisoners at Guantánamo Bay.

[1][2] Following his time in the George W. Bush administration, Stimson joined The Heritage Foundation, where he is currently a senior legal fellow and manager of the National Security Law Program.

Earlier in his career, Stimson served as an Assistant United States Attorney for the District of Columbia and as Vice President for Private Equity Mergers & Acquisitions at Marsh & McLennan Companies.

[10] In January 2007, he made comments concerning the legal representation of Guantánamo detainees stating that "corporate CEOs seeing this should ask firms to choose between lucrative retainers and representing terrorists.

[3] Stimson is currently a senior legal fellow at The Heritage Foundation, a conservative think-tank, and an instructor at the Naval Justice School in Newport, Rhode Island.

[20] In September 2010 he authored a report, titled "Just Say No", asserting that California's proposed Regulate, Control and Tax Cannabis Act of 2010 would "worsen the state’s drug problems—addiction, violence, disorder, and death".