[3] Nelson was born in San Francisco, the son of Norwegian immigrants, Betsy (née Christophersen) and Trygve Nielsen.

[7] With MGM, Nelson made his screen debut in the role as Paul Clark in Shadow of the Thin Man (1941) starring William Powell and Myrna Loy, with Donna Reed.

[9] During his service in the United States Army Air Forces during World War II, Nelson debuted on the Broadway stage in Moss Hart's play Winged Victory (1943) in the role of Bobby Grills.

He also appeared with Lauren Bacall in the Abe Burrows comedy Cactus Flower in 1965[2] and with Dorothy Loudon in The Fig Leaves Are Falling in 1969.

[10] He was the first actor to play James Bond on screen in a 1954 adaptation of Ian Fleming's novel Casino Royale on the television anthology series Climax!

[9] Reportedly this was considered a pilot for a possible James Bond television series, though it is not known if Nelson intended to continue playing the character.

"[11] Bond did not become well known in the U.S. until President John F. Kennedy listed From Russia, with Love among his 10 favorite books in a March 17, 1961, Life article.

[8] Nelson had a notable role as Stuart Ullman, the manager of the Overlook Hotel, in the Stanley Kubrick horror film The Shining (1980).