He began his legal career by serving as a law clerk to Judge Leonard B.

From 1981 to 1983, he worked at Harvard Law School's Center for Criminal Justice as a research associate and special investigator.

From 2004 to 2016, he served as an associate justice of the Massachusetts Appeals Court adjudicating civil and criminal matters.

[1][2] His twin brother, Robert Katzmann, served as chief judge on the United States Court of Appeals for the Second Circuit.

[3] On July 30, 2015, President Barack Obama nominated Katzmann to serve as a United States Judge of the United States Court of International Trade, to the seat vacated by Judge Jane A. Restani, who took senior status on March 1, 2015.