Morrison then entered government service, working as a Deputy Assistant Attorney General for Review and Appellate Matters in the Tax Division of the United States Department of Justice, from September 2001 to August 2008 (except for term as Acting Assistant Attorney General, from July 2007 to January 2008). Nominated by President George W. Bush as Judge, United States Tax Court, on November 15, 2007, Morrison was confirmed by Senate, July 7, 2008. Following confirmation he was then appointed by President George W. Bush as a Judge of United States Tax Court, on August 28, 2008, for a term ending August 27, 2023.