Promoted in 2001, McMahon served twelve years as a lieutenant and worked as a watch commander, administrative lieutenant, detective commanding officer, and as the Officer in Charge when Operations- Valley Bureau first implemented the Violent Crime Task Force. He worked extensively with retailers, local businesses and community leaders on crime prevention initiatives.
Additionally, he has served as an Assistant Watch Commander to the patrol operations team in Wilshire Area, supervised a staff responsible for preparing directives regarding Department policy and procedures for the Chief of Police and was also assigned to Internal Affairs as a member of the Rampart Corruption Task Force.
Raised in Southern California, McMahon was originally inspired to join the Department by his father, a World War II Army veteran, who greatly admired the Los Angeles Police Department. Commander McMahon holds a BA in Business Administration from the University of LaVerne, and is a graduate of the West Point Leadership Academy.