From 2010 to 2012, he served as special advisor to the U.S. Department of State’s Legal Adviser, Harold Hongju Koh. Previously, Pozen clerked for Justice John Paul Stevens on the U.S. Supreme Court (2009-2010) and for Judge Merrick B. Garland on the U.S. Court of Appeals for the D.C. Circuit (2008-2009). From 2007 to 2008, Pozen served as special assistant to Senator Edward M. Kennedy on the Senate Judiciary Committee.