 Matsumoto was a private practice attorney in Washington state from 1981 to 1983 before joining the United States Attorney's Office as Assistant United States Attorney for the Eastern District of New York from 1983 to 2004.Matsumoto served as an Adjunct Professor of Law at New York University School of Law from 1998 to 2004.From 2004 to 2008, Matsumoto served as a United States Magistrate Judge in the Eastern District of New York.