As Crisis Group's chief of policy, Stephen works with regional and cross-cutting programs to develop and promote the organisation’s analysis and prescriptions. He is based in Washington D.C.

Prior to joining Crisis Group, Stephen served as special assistant to the president and senior director for Multilateral Affairs and Human Rights at the National Security Council under President Obama. Prior to joining the staff of the National Security Council, he served in a variety of roles with the Office of the Legal Adviser at the U.S. Department of State, where he specialised in domestic and international law regulating the use of force and the law of war, including as the assistant legal adviser for Political-Military Affairs.

Outside government, Stephen has been a senior policy scholar at the U.S. Institute of Peace and a Leonard and Sophie Davis Genocide Prevention distinguished fellow at the U.S. Holocaust Memorial Museum, and was in private practice at Cleary, Gottlieb, Steen & Hamilton. He is a non-residential senior fellow at the NYU Law School Reiss Center on Law and Security. Stephen received his undergraduate degree from Harvard College and his law degree from Yale Law School.