A native of Huntington, New York, Mills graduated from Franklin and Marshall College with a BA in political science and a minor in history[2] and was commissioned in 1975 as a second lieutenant via Officer Candidate School.

He later attended the Marine Corps Command and Staff College, then spent a year as a Military Observer with the United Nations in Palestine.

[3] He was selected to command the 24th Marine Expeditionary Unit (Special Operations Capable) in 2000 and promoted to colonel.

[3][4] In June 2003 Colonel Mills reported to Headquarters, United States European Command in Stuttgart, Germany, as the assistant chief of staff.

[4] He was promoted to major general in late 2007 and from October 2007 to January 2009 served in a dual role as assistant division commander, 1st Marine Division and commander, Ground Combat Element, Multi-national Forces – West in Al Anbar Province, Iraq.

[9] He currently serves as president and chief executive officer of the Marine Corps University Foundation.

[10] Lieutenant General Mills has a reputation for having a good sense of humor and being open to subordinates, officers have told reporters.