In 1956–1957, Metcalfe was drafted as an enlisted man into the United States Navy, serving two years. He was stationed at Ream Field, San Ysidro, California, where he held a public relations position. During this period, Metcalfe acting as the lead, working closely with some of his fellow enlisted comrades created the "Miss Angel" beauty contest. An "Angel" in Navy terms meaning a helicopter that would swoop in saving downed pilots who ditched their aircraft in the sea and in some cases on land. Ream Field at that time was virtually the "helicopter capitol of the world".
In 1959, Metcalfe had a small role in the movie Gidget, as Lord Byron, the existentialist surfer, hanging 10 with The Big Kahuna's crew. That same year, he was cast as Tom Easton, a young United States Army officer, in the episode "Indian Emily" on the syndicated television anthology series, Death Valley Days, hosted by Stanley Andrews. At Fort Davis, Texas, Emily (Jolene Brand), an Apache captive, adopts the white man's ways but flees from the fort when Easton, whom she loves prepares to marry another. She returns to warn the fort of a pending Apache attack and after saving the fort died of a gunshot wound fired in error. Meg Wyllie played Tom's compassionate mother, Mrs. Easton. A memorial has been erected at Fort Davis to honor the heroism of Indian Emily. 
Metcalfe was cast as Don Martin, one of the neighbors thrown into a panic in Rod Serling's The Twilight Zone episode titled "The Monsters Are Due On Maple Street" which aired on March 4, 1960, season 1, episode 22 (imbd.com).
In 1960–1961, Metcalfe landed an acting role as Joe Brigham in the NBC sitcom Happy, starring Ronnie Burns as the manager of a Palm Springs, California, hotel and the father of a talking baby nicknamed "Happy". Between 1962 and 1965, Metcalfe made three guest appearances on Perry Mason: as Richard Campion in "The Case of the Polka-Dot Pony," murderer John Lathrop in "The Case of the Careless Kidnapper," and Jeffrey Mills in "The Case of the Thermal Thief."
His most notable work was as a writer for the hit CBS series M*A*S*H, and he was the only producer to stay with the TV series during its entire run from 1972 to 1983. Originally the series' associate producer, Metcalfe was promoted to line producer in 1976 when Larry Gelbart left the series and then to executive producer in 1977, when Gene Reynolds moved on to become executive producer for the CBS-TV series Lou Grant.
Metcalfe also served as the executive producer for the M*A*S*H 30th Anniversary Reunion Special which aired on FOX in September 2002.
- The Bridges at Toko-Ri (1954) - Military Police Sergeant (uncredited)
- The Space Children (1958) - Guard (uncredited)
- Gidget (1959) - Lord Byron
- Don't Give Up the Ship (1959) - Lt. Bond (uncredited)
- The Canadians (1961) - Constable Springer
- Diamonds Are Forever (1971) - Maxwell (uncredited)
- The Twilight Zone (1960) - Don Martin (The Monsters Are Due on Maple Street)