It was during the '60s and 70s, however, that O'Loughlin would become virtually ubiquitous on TV, his workload decreasing only slightly during the century's final two decades. One of his early guest-starring roles was on ABC's Going My Way, based on a 1944 film.
After a stint with the United States Marine Corps, O'Loughlin used his GI Bill of Rights benefits to train at the Neighborhood Playhouse in New York City. Continuing to hone his skills at the Actors Studio, he would land a handful of TV and/or film roles throughout the 1950s.
O'Loughlin appeared in an episode of the 1961 television series The Asphalt Jungle. He appeared in three episodes of Hawaii Five-O. The first was aired January 29, 1969 in the episode "The Box". O'Loughlin played the tough but sympathetic central figure of a group of prison inmates who take Hawaii Five-O chief Steve McGarrett (Jack Lord) hostage. The second was called "Six Kilos" on March 12, 1969 (playing the same character as in "The Box"), and the third was called "A Time to Die" on September 16, 1970. He also appeared on Cannon on February 22, 1972, in the episode "Flight of the Hawks". He also appeared on episode 16 of the TV show The Green Hornet. In Season 2 Episode 22 of Mission:Impossible, he played a killer for hire.
In 1970-1971, O'Loughlin portrayed Devin McNeil in the CBS crime drama Storefront Lawyers (which was revised and became Men at Law).
From 1972 to 1976 O'Loughlin appeared as Lt. Ed Ryker on The Rookies. He has also appeared in semi-regular roles on the series Our House and Automan. In 1978, he appeared in the pilot episode of The Eddie Capra Mysteries, and had roles in TV miniseries such as Wheels (1978), Women in White (1979), Roots: The Next Generations (1979) and Blind Ambition (1979). He also appeared as Sgt. O'Toole in the 1983 made-for-TV miniseries The Blue and the Gray. In 1986, O'Loughlin played the part of Mr. Parks in a first season episode of Highway to Heaven entitled "The Brightest Star".
In 1988, he played Tom Callahan in Dirty Dancing. In 1992 he appeared as Ben Oliver in Murder She Wrote in the episode "Badge of Honor".
O'Loughlin and his wife Meryl Abeles O'Loughlin (1933–2007), had two children: Chris O'Loughlin (b. 1967), a member of the 1992 United States Olympic épée fencing team, and Laura O'Loughlin. O'Loughlin died of natural causes in Los Angeles on July 31, 2015.
