McClory portrayed the Irishman Jack McGivern, the man known for having the best timing around, in the first season of NBC's western television series, The Californians, set in the California Gold Rush of the 1850s. It aired from 1957 to 1959. His co-stars included Nan Leslie as Martha McGivern, Richard Coogan, Herbert Rudley and Adam Kennedy, the latter as newspaperman Dion Patrick.

In 1958, McClory was cast as Ted O'Malley in the episode "Short Haul" of the CBS crime drama, Richard Diamond, Private Detective, starring David Janssen. Nan Leslie appeared with McClory on this episode in the role of Ted's wife, Myrna O'Malley.

McClory appeared twice in the short-lived 1960 NBC western series, Overland Trail, starring william Bendix and Doug McClure. He was a guest star in the syndicated western series, Pony Express and in 1960 on ABC's western drama, The Man from Blackhawk, starring Robert Rockwell as a roving insurance investigator. Another 1960 role was as Quinn in "Talent for Danger" on the ABC adventure series, The Islanders, set in the South Pacific. In 1960 and 1961, McClory appeared in the episodes, "Heads, You Lose" and "Appointment at Tara-Bi", of another ABC series, Adventures in Paradise, starring Gardner McKay. In 1961 and 1962, McClory was a guest star in episodes of the television Western The Rifleman, the 1961 episode "Knight Errant" in which he shared the guest star role with 3 other guest stars, one being late western film and TV icon Jack Elam. In 1962 McClory was the spotlight guest star of episode "I Take This Woman" playing an Irish romantic rival to star Chuck Connors' lead character of Lucas McCain.

McClory appeared as Jaimie MacDonald in the 1963 episode "Commando" of the CBS anthology series, GE True, hosted by Jack Webb. He was cast thereafter in a second-season episode of Irwin Allen's CBS science fiction series Lost in Space called "The Astral Traveller", as a Scottish bagpiping "ghost" named Hamish. He made several guest appearances on Perry Mason, including the 1961 episode, "The Case of the Malicious Mariner", the defendant in the 1962 episode, "The Case of the Unsuitable Uncle," and the title character and husband of the defendant in "The Case of the Scandalous Sculptor." McClory made two appearances on NBC's Bonanza, as Mark Connors in the 1962 episode "The Tall Stranger" and as Professor James Aloysuis McCarthy in the 1963 comedic episode "Hoss and the Leprechauns".

In 1965, McClory was cast as the poet Joaquin Miller, with June Lockhart (who had played his wife in the Perry Mason episode “The Case of the Scandalous Sculptor”) in the role of Ina Coolbrith, first poet laureate of California, in the episode "Magic Locket" of the syndicated western series, Death Valley Days, hosted by Ronald W. Reagan. In the story line, Coolbrith develops a tenuous friendship with the teen-aged "Dorita Duncan" (Kathy Garver), later known as the Dancer Isadora Duncan. The two have identical portions of a broken locket.

Sean played Scott Winters in CBS's Mannix episode entitled "Then the Drink Takes the Man", first aired on 30 December 1967.