Prior to that, he had guest-starring roles on a number of popular series, such as Sea Hunt, several episodes of Zane Grey Theatre, Wagon Train, Have Gun, Will Travel, 77 Sunset Strip and Gunsmoke.
The first movie in which Breck was the top-billed star was Lad: A Dog (1962). The next year he played the leading roles in both Shock Corridor and the sci-fi horror film The Crawling Hand. During this timeframe he also made appearances on episodes of several more TV shows, such as The Outer Limits, Bonanza, Perry Mason, and The Virginian.
From 1965 to 1969 he starred in the TV western series The Big Valley.
Most of his roles in the 1970s and 1980s were more TV guest-starring performances, on series such as Alias Smith and Jones, Mission: Impossible, McMillan and Wife, S.W.A.T., The Six Million Dollar Man, The Incredible Hulk, and Dukes of Hazzard, as well as roles as himself on Fantasy Island and The Fall Guy.
In the mid-1980s, Peter moved to Vancouver, British Columbia, Canada with his wife Diane, and son Christoper. He was asked by a casting director to teach one class a week to young actors on film technique. That one a week class became a full time acting school - The Breck Academy - which he ran for 10 years. In 1990 Breck appeared in the Canadian cult film Terminal City Ricochet.
In 1996 he appeared in an episode of the new version of The Outer Limits.
His most recent TV performance was on an episode of John Doe in 2002. In recent years most of his movie performances have been in undistributed films that are only shown at film festivals.