Larsen was born in Salt Lake City in 1924. He was of Norwegian descent. During World War II, he served in the United States Navy. After he was demobilized he became involved in stage acting in Santa Monica, California.

Larsen was tapped by a talent scout to play a small uncredited role in 1951 movie Operation Pacific. In 1952, Larsen played Ens. Barney Smith, an aircraft carrier fighter pilot, in the film Flat Top. In 1953, Larsen played the title role of Ed Reed, the Kid in the film Son of Belle Starr, in which his character tries to live an upright life despite the heritage of his two lawless parents, Belle Starr and Jim Reed.

Larsen's career was most notable for his work in four weekly television series, including playing Bart Adams in The Hunter (1954), Brave Eagle (1955), Northwest Passage (1958) (in which he starred as Major Robert Rogers), and The Aquanauts (1960).

In the 1955–1956 television season, Larsen starred in the 26-week CBS western Brave Eagle. Larsen portrayed Brave Eagle, a peaceful young Cheyenne chief. The program was unusual in that it reflected the Native American viewpoint in the settlement of the American West. Larsen's principal co-stars were Kim Winona (1930–1978) as Morning Star, Anthony Numkena, a Hopi Indian then using the stage name Keena Nomkeena, as Keena, Brave Eagle's foster son, and Bert Wheeler (1895–1968) as Smokey Joe.

He guest starred in 1957 on three CBS programs, as Paul in the "Anitra Dellano Story" of The Millionaire, and in two anthologies, as Howard in "The Blackwell Story" on Playhouse 90, and as Eddie Seabord in the episode "Father and Son Night" on General Electric Theater, hosted by Future U.S. President Ronald W. Reagan.

In the 1958–1959 season, Larsen starred in the M-G-M/NBC series Northwest Passage, the story of Major Robert Rogers, an American soldier in upstate New York during the French and Indian War. Buddy Ebsen co-starred as Sergeant Hunk Marriner and Don Burnett as Ensign Towne. In 1959, Larsen guest starred on the CBS series Men into Space in the role of Jim Nichols in the episode " Christmas on the Moon".

Larsen was married three times. In 1953, he wed Actress Susan Cummings. They have one child. After their divorce, he married Actress Vera Miles on July 16, 1960. He was married to Vera Miles until 1971. Their son, Erik Larsen, was born in April 1961. After Larsen and Miles divorced, he married Trang Thu Nguyen in 1983. The couple had one child. The marriage ended when Larsen died, aged 82, in Santa Barbara, California.

After The Aquanauts, Larsen appeared as Jack Bennett in the 1961 episode "Blondes Prefer Gentlemen" of the ABC series The Roaring Twenties, with Donald May, Rex Reason, and Dorothy Provine. His other television roles, all in 1960, were as John Edwards in "The Hostage" episode of the ABC and syndicated western series, Tombstone Territory, as John Napier in "Nightmare Crossing" episode of NBC's The Man and the Challenge, and as the Indian, Blue Raven, in the episode "Seed of Hate" in NBC's western Wichita Town.

Larsen's later acting work was in films: Women of the Prehistoric Planet (1966), The Omegans (1968) with Ingrid Pitt, Mission Batanagas as Colonel Turner (1968), Night of the Witches as Reverend Ezra Jackson (1970), The Trap on Cougar Mountain (1972), Whitewater Sam in the title role (1977), and his last appearance, Young and Free (1979). He also directed and produced some of these same films.