Chief Milligan joined the Rumford Police in January 1988 at age 20 as a Patrolman. He became the department's youngest Sergeant and the first to transition from being a "desk sergeant" to a shift commander not tied to a desk, working from the station and out on the road.

In 1992, Milligan was placed on temporary assignment to the Maine Drug Enforcement Agency where he served as a Special Agent and Deputy Supervisor for 27 years working as an undercover agent conducting felony drug investigations primarily in Western Maine.

In January 2020, Milligan retired from drug enforcement and returned to Rumford PD to accept the appointment to Chief of Police.