Thomas Donnelly is an American defense policy expert and neoconservative intellectual known for his influential work on U.S. national security and military strategy. He has held prominent positions at major think tanks, including as a resident fellow at the American Enterprise Institute (AEI) from 1999 to 2010, where he specialized in defense budgeting, military transformation, and U.S. foreign policy toward regions like the Middle East and East Asia. Prior to AEI, Donnelly worked as a senior fellow at the Center for Strategic and International Studies (CSIS) and served in various roles related to defense analysis, including as a professional staff member for the House Armed Services Committee. His career has focused on advocating for increased military spending and a proactive U.S. global posture.

Donnelly co-founded the Project for the New American Century (PNAC) in 1997, serving as its deputy executive director until its dissolution in 2006. PNAC, a neoconservative advocacy group, played a pivotal role in shaping the intellectual groundwork for the Iraq War and the Bush administration's foreign policy through reports like 'Rebuilding America's Defenses' (2000) and open letters urging regime change in Iraq. He co-authored several key publications, including 'The Under Secretary: The Army and the Future of Defense' (2002) and contributions to neoconservative journals such as The Weekly Standard. Donnelly's writings have often emphasized the need for U.S. primacy and criticized perceived weaknesses in American defense policy.

Post-AEI, Donnelly has continued as an independent consultant, writer, and commentator on defense issues, contributing to outlets like National Review and appearing in media discussions on military affairs. His staunch support for interventionist policies, including the Iraq War, has drawn criticism from anti-war advocates and progressives, who accuse him of promoting aggressive neoconservative agendas. Despite controversies, his expertise remains cited in debates on U.S. strategy.