Ermey spent two years as a drill instructor at the Marine Corps Recruit Depot in San Diego, California, and Parris Island, South Carolina from 1965 to 1967. In 1968, Ermey arrived in Vietnam where he served for 14 months with the Marine Wing Support Group 17. He then served two tours of duty in Okinawa, Japan, during which he rose to the rank of Staff Sergeant (E-6) and was medically retired in 1972 for several injuries incurred during his tours.

when he was cast as tough drill instructor Gunnery Sergeant Hartman in Stanley Kubrick's Full Metal Jacket; Ermey also served as the technical advisor on the film. Initially, he was only intended to be the technical advisor, but Kubrick changed his mind after Ermey put together an instructional tape to convince Kubrick he was the right person for the role, in which Ermey went on an extended hair-raising drill instructor tirade towards several Royal Marines cast as extras, all the while being pelted by oranges and tennis balls, and managing to do so without repeating himself, stopping, or even flinching. Kubrick allowed him to write his own dialogue and improvise on set, a noted rarity in a Kubrick film. Kubrick later indicated that Ermey was an excellent performer, often needing just two or three takes per scene, also a noted rarity for a Kubrick film. Ermey's performance won critical raves and he was nominated for a Golden Globe Award as Best Supporting Actor.