Born in Teaneck, New Jersey, he was the younger son of Ozzie Nelson, the leader of a big band, and Harriet Hilliard Nelson, the band's singer.
Along with brother David Nelson, the family starred in the long-running radio and television series The Adventures of Ozzie and Harriet from 1944 to 1966; until 1949, the sons were played on radio by professional actors.
His twin sons, Gunnar and Matthew Nelson, also were teen idols, performing as Nelson, and his daughter Tracy Nelson is an actress and cancer survivor.