He was a senior counsel to the United States Senate Committee on Governmental Affairs in 1997.

He was the United States Attorney for the Eastern District of Tennessee from 2001 to 2005.

On July 28, 2005, Mattice was nominated by President George W. Bush to a seat on the United States District Court for the Eastern District of Tennessee vacated by Robert Allan Edgar.

Mattice was confirmed by the United States Senate on October 24, 2005, and received his commission on November 18, 2005.

On October 8, 2019, Mattice announced his intent to take senior status on March 10, 2020.