Assistant Police Chief John McKean was born and raised in Detroit, Michigan. Immediately after high school graduation in 1982, he enlisted in the United States Marine Corps and served honorably for the next twenty years, retiring as a First Sergeant. While still on active duty, McKean attended the Palomar Police Academy from July 2000 to September 2001. After graduating from the academy in 2001, Assistant Chief McKean started his career with the Oceanside Police Department as a Level 1 Reserve Officer. After he retired from the Marines, he joined the Oceanside Police Department as a regular officer in August 2003. McKean holds a Bachelor of Science in Criminal Justice from Union Institute and University and a Master of Science in Law Enforcement and Public Safety Leadership from the University of San Diego. He is also a graduate of the FBI Nation Academy session #284.

During his time at the Oceanside Police Department, Assistant Chief McKean has had assignments in Patrol, the Gang Suppression Unit, the Special Enforcement Section, North County Regional Gang Task Force, and Detective Sergeant in the Property Crimes and Financial Crimes Unit, the Special Weapons and Tactics Team, and the Crisis Negotiator Team, both as a Negotiator and a Supervisor. Before his current rank, McKean was the Support Operations Division Lieutenant.  In April 2023, he was promoted to Investigations Division Captain.  In December 2024,  John McKean was selected as the Assistant Chief of Police.