A veteran of overseas deployment to Africa during the Global War on Terrorism, he was most notable for high-profile command assignments including Joint Task Force – Civil Support (2012–2014) and I Corps (2009–2010).

[1] Mathis was a member of the Florida Army National Guard when he completed Officer Candidate School and received his commission as a second lieutenant of Infantry.

[4] In February 1989, Mathis joined the New York Army National Guard and was assigned as assistant human resources officer (G-1) on the staff of the 42nd Infantry Division.

[4] In December 1992, he was assigned as chief of the training section for Operations Readiness Evaluation Team 1, Sixth United States Army at the Presidio of San Francisco, California, where he remained until September 1993.

[4] Mathis attended the United States Army Command and General Staff College at Fort Leavenworth, Kansas from July to December 1995.

[4] Mathis served as deputy commander and chief of staff for Combined Joint Task Force – Horn of Africa in Djibouti from October 2003 to June 2004.

[4] Mathis served as director of the Joint Staff for the Washington National Guard from August 2006 to June 2008, and was promoted to brigadier general in May 2007.

[4] In 2008, he completed the Senior Commander's Course at Fort Belvoir, Virginia and the Army Strategic Leadership Development Program - Intermediate at the University of North Carolina at Chapel Hill.

[4] In 2009, Mathis graduated from the Senior Executive Seminar at the George C. Marshall European Center for Security Studies in Garmisch-Partenkirchen, Germany.

[4] In January 2011, Mathis was promoted to major general, and later that year he graduated from the National Defense University's CAPSTONE program at Fort Lesley J. McNair in Washington, D.C.[4] In July 2012, Mathis was assigned to command Joint Task Force – Civil Support at Fort Eustis, Virginia and he remained in this position until retiring in July 2014.