He currently hosts Mail Call, a military history program on The History Channel.

On May 17, 2002 he received an honorary promotion to Gunnery Sergeant (E-7) by the then Commandant of the Marine Corps, James L. Jones, becoming the first retiree in the history of the Marines to be promoted.

Born in Emporia, Kansas, Ermey enlisted in the United States Marine Corps in 1961. Ermey had been arrested several times as a teenager and the judge gave him a choice of the military or jail. He later joked that the Marine Corps "put a screeching halt to my unconventional manner".

He spent two years as a drill instructor at Marine Corps Recruit Depot San Diego in San Diego, California 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 that time, Ermey rose to the rank of Staff Sergeant and was medically discharged in 1972 for several injuries received during his tours. He did not receive a Purple Heart due to his injuries being non-combat in origin. Ermey has admitted that he still has nightmares about his combat experiences, a symptom of post-traumatic stress disorder. Ermey was later bestowed with the honorary rank of Gunnery Sergeant by the Marine Corps.

Ermey was cast in his first movie while he studied at the University of Manila in the Philippines, using his G.I. Bill benefits. He played a helicopter pilot in Apocalypse Now; he also served as a technical advisor to director Francis Ford Coppola on that film. He played minor roles in films until 1987, when he was cast as the tough drill instructor Gunnery Sergeant Hartman in Stanley Kubrick's Full Metal Jacket; Ermey also served as the technical advisor on the film.

He was originally supposed to be just the technical advisor to the film, but Kubrick changed his mind after hearing Ermey's hair raising DI tirades, and even let him write some of his dialogue and improvise on set. Kubrick later stated that Ermey was one of the best actors he had ever worked with, needing just two or three takes per scene. The performance won critical raves and Ermey was nominated for a Golden Globe Award as Best Supporting Actor. He would later play a tough Drill Instructor in the pilot episode of Space Above and Beyond and in the film The Frighteners, both similar to his character in Full Metal Jacket.

He has appeared in approximately sixty films, including Mississippi Burning, Dead Man Walking, Se7en, Leaving Las Vegas, Prefontaine, Saving Silverman, Man of the House, and the remakes of Willard and The Texas Chainsaw Massacre as both sneering villains. Ermey also lent his voice for Toy Story and Toy Story 2, as well as Roughnecks. He has appeared on television in shows including The Simpsons, Family Guy, Miami Vice, House, Scrubs and Invader Zim.

In addition to his film and television credits, Ermey has lent his distinctive voice to several video games, including Fallout Tactics: Brotherhood of Steel and Crash Bandicoot: The Wrath of Cortex. He also made a cameo in Real War: Air, Land, Sea.