John Allen Nelson was born on August 28, 1959 in San Antonio, Texas and moved to Germany when he was a few weeks old. It was the first of many moves for John, whose dad was in the Air Force. As a young man, John went to New York to pursue acting. Before originating the role of Warren Lockridge on Santa Barbara, he trained at Joanne Woodward's acting workshop.

After leaving SB, John starred as the title character in the 1987 film Hunk and this was followed by movies like Saigon Commandos, Deathstalker III and Killer Klowns from Outer Space.

His notable TV credits include Baywatch, Sheena and Privileged. He is perhaps best known for playing Walt Cummings in 24 and Senator Jeffrey Collins in the drama Vanished.

John co-wrote the screenplay for the film Best of the Best 2, which was released in 1993, as well as American Yakuza starring Viggo Mortensen. In 1994, John co-wrote and co-starred in the movie Criminal Passion.

John is married to actress Justine Eyre. They have a son together. John's two children from his previous marriage live with their mother in Sweden.