| Year | Title | Role | Notes |
|---|
| 1956 | Matinee Theatre | — | 4 episodes |
| 1957–1961 | Wagon Train | Will Santee / Rodney Lawrence / Juan Ortega / Jimmy Drew |
| 1958 | Cimarron City | Bud Tatum | Episode: "Kid on a Calico Horse" |
| 1959 | Buick-Electra Playhouse | Nick Adams | Episode: "The Killers" |
| Johnny Staccato | Dave | Episode: "Nature of the Night" |
| 1960 | Checkmate | Roddy Stevenson | Episode: "Cyanide Touch" |
| The DuPont Show with June Allyson | Johnny Perry | Episode: "The Dance Man" |
| 1961 | The Twilight Zone | Lt. Katell | Episode: "A Quality of Mercy" |
| Alfred Hitchcock Presents | Billy Weaver | Season 6 Episode 19: "The Landlady" |
| 1962 | The Alfred Hitchcock Hour | David H. Kelsey / William Newmaster | Season 1 Episode 7: "Annabel" |
| 1963 | Combat! | Rob Lawson | Episode: "High Named Today" |
| 1964 | Kraft Suspense Theatre | Martin Rosetti | Episode: "Their Own Executioners" |
| 1965 | Dr. Kildare | Dr. Rudy Deveraux | 6 episodes |
| 1969 | Bonanza | Matthew Rush | Episode: "The Medal" |
| 1971 | Mannix | Chris Townsend | Episode: "A Step in Time" |
| Paper Man | Avery Jensen | Television film |
| The Failing of Raymond | Raymond |
| 1972 | Adventures of Nick Carter | Freddy Duncan | Pilot |
| Columbo | Eric Wagner | Episode: "The Most Crucial Game" |
| 1973 | Mission: Impossible | Gunnar Malestrom | Episode: "The Pendulum" |
| Night Gallery | Charlie Evans | Episode: "Whisper" |
| The Streets of San Francisco | Paul Thomas | Episode: "Legion of the Lost" |
| Orson Welles Great Mysteries | Jerry | Episode: "Unseen Alibi" |
| 1975 | Police Story | Ott / Detective Giacino / Detective Callan / Bennett | 4 episodes |
| Cop on the Beat | Det. Callan | Television film |
| Columbo | Lloyd Harrington | Episode: "Troubled Waters" |
| Cannon | Tom Longman | Episode: "The Hero" |
| Ellery Queen | Cliff Waddell | Episode: "The Adventure of the Blunt Instrument" |
| Three for the Road | Ethan Crawford | Episode: "The Trail of Bigfoot" |
| 1976 | McCloud | Pete Lancaster | Episode: "'Twas the Fight before Christmas" |
| 1977 | A Killing Affair | Kenneth Switzer | Television film |
| Quinn Martin's Tales of the Unexpected | Richard Ayres | Episode: "No Way Out" |
| 1978 | Greatest Heroes of the Bible | Hissar | Episode: "Daniel in the Lion's Den" |
| 1981 | Born to Be Sold | Marty Helick | Television film |
| 1982 | Hart to Hart | James Francis | Episode: "Harts' Desire" |
| 1983 | The A-Team | Officer Collins | Episode: "A Small and Deadly War" |
| 1985 | Miami Vice | Jack Gretsky | Episode: "Bushido" |
| 1986 | Hunter | Brother Harold Hobarts | Episode: "Bad Company" |
| 1987 | The Gambler, Part III: The Legend Continues | James McLaughlin | Television film |
| 1988 | Murder, She Wrote | Eliot Easterbrook | Episode: "Deadpan" |
| 1989–1993 | Quantum Leap | Admiral Al Calavicci | 97 episodes |
| 1989 | The Twilight Zone | Martin Decker | Episode: "Room 2426" |
| 1990–1992 | Captain Planet and the Planeteers | Duke Nukem | Voice, 9 episodes |
| 1991 | Son of the Morning Star | General Philip Sheridan | Miniseries |
| 1992 | Roseanne | Ralph | Episode: "Breaking Up Is Hard to Do" |
| 1993 | Bonanza: The Return | Augustus Brandenburg | Television film |
| 1994 | Vanishing Son II | Mickey Jo Valmont |
| Justice in a Small Town | Commissioner Sam Caldwell |
| The Innocent | Capt. Jason Flaboe |
| Madonna: Innocence Lost | Tony Ciccone |
| In the Line of Duty: The Price of Vengeance | Jack Lowe |
| Chicago Hope | Robert St. Clair | Episode: "Songs from the Cuckoo Birds" |
| Lois & Clark: The New Adventures of Superman | Preston Carpenter | Episode: "The Rival" |
| 1995 | The Langoliers | Bob Jenkins | 2 episodes |
| The Man from Snowy River | Professor Julius Waugh |
| Nowhere Man | Gus Shepherd | Episode: "You Really Got a Hold on Me" |
| 1996 | Unabomber: The True Story | Ben Jeffries | Television film |
| 1997–1998 | The Tony Danza Show | Frank DiMeo | 14 episodes |
| 1998 | It's True | Mr. Murphy | Pilot |
| 1998–1999 | Phenomenon: The Lost Archives | Host | 14 episodes |
| 1999 | What Katy Did | Tramp | Television film |
| The Drew Carey Show | Hal | Episode: "Y2K, You're Okay" |
| 2002–2004 | JAG | Edward Sheffield, SecNav | 11 episodes |
| 2002 | First Monday | Senator Edward Sheffield | 3 episodes |
| Star Trek: Enterprise | Colonel Grat | Episode: "Detained" |
| Stargate SG-1 | Doctor Kieran | Episode: "Shadow Play" |
| 2006–2009 | Battlestar Galactica | John Cavil / Number One Cylon | 15 episodes |
| 2008 | Crash | Frankie Navajo | Episode: "Los Muertos" |
| 2009 | The Dunwich Horror | Dr. Henry Armitage | Television film |
| Battlestar Galactica: The Plan | John Cavil / Number One Cylon |
| 2014 | Enlisted | Dan | Episode: "Vets" |
| NCIS: New Orleans | Tom Hamilton | Episode: "Chasing Ghosts" |