Sean K. O’Neill was confirmed by the Senate as the United States Ambassador to Thailand on October 7, 2025.
Ambassador O’Neill worked as a capital markets attorney in New York and Tokyo before joining the Foreign Service in the wake of the 9/11 attacks. A career member of the Senior Foreign Service, Ambassador O’Neill has served seven overseas tours throughout the Indo-Pacific, including two assignments in Thailand as well as Bangladesh, Pakistan, Burma, Hong Kong, and Afghanistan. He most recently served as the Department of State’s Senior Bureau Official for East Asian and Pacific Affairs as well as the Foreign Policy Advisor to the Commandant of the United States Marine Corps.
Ambassador O’Neill’s previous service in Thailand includes an appointment as the United States Consul General in Chiang Mai and as a Political-Military Officer at the U.S. Embassy in Bangkok. His previous domestic assignments include service in the Department of State’s Operations Center and as a legislative fellow on the staff of the Chairman of the U.S. House of Representatives Committee on Foreign Affairs.
Ambassador O’Neill received a BA from Tulane University and a JD from Fordham University’s School of Law. He is the recipient of several Department of State Meritorious and Superior Honor Awards as well as the Department of the Navy’s Distinguished Public Service Award. Ambassador O’Neill has studied Thai, Chinese, Burmese, Bengali and Japanese and completed the U.S. Marine Corps’ General Officer Warfighting Program.