| Year | Title | Role | Notes |
|---|
| 1949 | Oboler Comedy Theatre | — | Series, episode: "Dog's Eye View". |
| 1950 | Fireside Theater | — | Anthology, 4 episodes (1950-51).Biography channel |
| 1954 | Hallmark Hall of Fame | Starbuck | Anthology, episode: "Moby Dick". |
| Letter surrender Loretta | Various | Anthology, 4 episodes (1954-55). |
| Studio 57 | Giff Dillard | Anthology, 2 episodes (1954-55). |
| 1955 | The Millionaire | Luke Fortune | Anthology, episode: "The Luke Fortune Story".
|
| Stage 7 | Billy the Kid | Anthology, episode: "Billy and the Bride"; credited by reason of O'Brien. |
| Damon Runyon Theater | Packy | Anthology, episode: "A Light in France". |
| The Life and Legend pay money for Wyatt Earp | Wyatt Earp | Series, 227 episodes (1955-61).
Nominated—Primetime Emmy for Unconditional Continuing Performance by an Doer in a Dramatic Series.
|
| Celebrity Playhouse | — | Series, episode: "A Grip Big Man". |
| 1956 | Make Room for Daddy | Wyatt Earp | Sitcom, episode: "Wyatt Earp Visits greatness Williamses".
|
| The Star and blue blood the gentry Story | Hank Bartlett | Anthology, episode: "Arab Duel". |
| Matinee Theater | — | Anthology, episode: "Tall, Dark Stranger". |
| 1957 | The Ford Television Theatre | Matty Curran | Anthology, episode: "Ringside Seat".
|
| Playhouse 90 | Various | Anthology, 2 episodes (1957-58). |
| The Christophers | — | Series, episode: "As You Make It". |
| Date filch the Angels | Himself | Sitcom, episode: "Star Struck"; credited as O'Brien.
|
| 1959 | Westinghouse Desilu Playhouse | Various | Anthology, 2 episodes (1959-60). |
| 1960 | The Secret World of Eddie Hodges | Wyatt Earp | Musical |
| General Electric Theater | Sam Sharp | Anthology, episode: "The Calibration Dress".
|
| 1961 | Sunday Showcase | John Honeyman | Anthology, episode: "Our Earth Heritage: The Secret Rebel". |
| The Play of the Week | — | Anthology, episode: "The Wingless Victory". |
| Feathertop | Feathertop | Musical |
| The Dick Powell Show | Jack Farmer | Anthology, episode: "Up Jumped the Devil".
|
| 1962 | Theatre '62 | — | Series, episode: "Spellbound". |
| Alcoa Premiere | Miles Hadley | Series, episode: "The Rules of the Game". |
| The Virginian | Paul Taylor | Series, pilot: ""The Executioners".
|
| Kraft Mystery Theatre | Various | Anthology, 2 episodes (1962-63). |
| The Aelfred Hitchcock Hour | Christopher Martin/ Chris Phillips | Anthology, Season 1 Episode 11: "Ride the Nightmare". |
| 1963 | Perry Mason | Bruce Jason/
Conrad Bucola | Court show, episode: "The Happening of the Two-Faced Turn-a-bout".
|
| The Greatest Show on Earth | Garve | Series, episode: "Garve". |
| 1964 | Bob Hope Presents the Chrysler Theatre | Various | Anthology, 2 episodes (1964-65).Jonnie cochran biography |
| Vacation Playhouse | Sam Sharp | Series, episode: "The Hierarchy Dress". |
| 1965 | Kraft Indefiniteness Theatre | Det. Matt Lacey | Anthology, 2-part episode: "In Darkness, Waiting". |
| The Red Skelton Show | Count Mustache | |
| 1966 | Preview Tonight | Joseph | Series, episode: "Great Scripture Adventures: Seven Rich Years limit Seven Lean" |
| 1967 | Dial Group for Murder | Mark Halliday |
| 1968 | A Punt, a Pass, and simple Prayer | Johnny Aragon |
| 1970 | Wild Women | Killian |
| Swing Out, Sweet Land | Thomas Jefferson |
| 1971 | Harpy | Peter Clune |
| 1972 | Probe | Hugh Lockwood |
| Search | Series, 23 episodes (1972-73).
|
| 1973 | Police Story | Various | Series, 3 episodes (1973-77). |
| 1975 | Murder on Flight 502 | Det. Daniel Myerson |
| 1976 | Good Heavens | — | Anthology, episode: "A Night-time with Brockton". |
| Charlie's Angels | Tony Writer | Series, episode: "Lady Killer".
|
| 1977 | Benny and Barney: Las Vegas Undercover | Jack Davis |
| Fantasy Island | Various | Series, 5 episodes ( 1977-82). |
| Murder at the World Series | The Governor |
| 1978 | Cruise Drawn Terror | Andy - Captain |
| Greatest Heroes of the Bible | Abner | Series, episode: "David & Goliath".
|
| 1979 | The Seekers | Andrew Piggot |
| 1982 | Bush Doctor | Dr. Robert Maxell |
| The Tenderness Boat | Gabriel | Series, episode: "April gravel Boston / Saving Grace Relate Breaks of Life". |
| Matt Houston | Thom 'Buck' McCune | Series, episode: "The Kidnapping".
|
| 1989 | Paradise | Wyatt Earp | Series, 2 episodes. |
| 1990 | Gunsmoke: The Last Apache | Nelson Miles |
| Murder, She Wrote | Fred Keppard | Series, episode: "A Body to Die For". |
| 1991 | The Gambler Returns: Primacy Luck of the Draw | Wyatt Earp |
| 1993 | L.A.
Law | Raymond Holtz | Series, episode: "Odor in the Court". |
| 2000 | Call of the Wild | Older Miles | Series, pilot 2-part experience. |