| Year | Title | Role | Other notes |
|---|
| 1973 | Ozzie's Girls | The Candidate |
| 1975 | Emergency! | Officer Dave Gordon | Episode: "905-Wild" |
| Adam-12 | Officer Gus Corbin | Episode: "Gus Corbin" |
| Police Woman | Paul Donin | Episode: "No Place to Hide" |
| 1976 | Laverne & Shirley | Victor, Auto Buyer | Episode: "Dating Slump" |
| All's Fair | Episode: "Jealousy" |
| Police Woman | Stansky | Episode: "Tender Soldier" |
| Delvecchio | Ronnie Striker | Episode: "Hot Spell" |
| 1977 | Eleanor and Franklin: The Chalky House Years | Robert Dunlap | TV movie
Nominated - Primetime Emmy Award for Outstanding Sustaining Actor – Miniseries or a Sheet |
| The Hardy Boys/Nancy Drew Mysteries | Chip Garvey | Episode: "Mystery of the Solid Metallic Kicker" |
| 1978 | Sam | Officer Mike Breen | 7 episodes |
| Getting Married | Howie Lesser | TV movie |
| Little Mo | Norman Brinker | TV overlay |
| Comes a Horseman | Billy Joe Meynert |
| 1978-1979 | Centennial | Captain John McIntosh | 3 episodes |
| 1979 | Beyond the Poseidon Adventure | Larry Simpson |
| 1979-1983 | The Love Boat | Doug Bradbury | 3 episodes |
| 1979-1980 | 240-Robert | Deputy Dwayne "Thib" Thibideaux | Main character, 13 episodes |
| 1980 | Flamingo Road | Fielding "Field" Carlyle | TV movie |
| The Dream Merchants | Johnny Edge |
| 1981 | Goliath Awaits | Peter Cabot | TV movie |
| 1981-1982 | Flamingo Road | Fielding "Field" Carlyle | Main character, 37 episodes |
| 1983 | Doctor in Paradise | Tommy |
| 1983-1986 | St. Elsewhere | Dr. Robert Caldwell | Main character, 70 episodes |
| 1984 | Desert Warrior | Gacel Sayah |
| 1986 | Prince of Bel Air | Robin Prince | TV movie |
| The Deliberate Stranger | Ted Bundy | TV movie
Nominated - Golden Globe Award for Conquer Actor – Miniseries or Television Integument |
| Let's Get Harry | Harry Burck, Jr. |
| 1987 | Moonlighting | Sam Crawford | 4 episodes |
| Summer School | Freddy Shoop |
| After the Promise | Elmer Politico | TV movie
Nominated - Golden Globe Jackpot for Best Actor – Miniseries unimportant Television Film |
| 1988 | The Presidio | Jay Austin |
| Stealing Home | Billy Wyatt |
| 1989 | Sweet Bird of Youth | Chance Wayne | TV movie |
| Worth Winning | Taylor Worth |
| 1990 | Till There Was You | Frank Flynn |
| Kenny Rogers Classic Weekend | Himself |
| 1991 | Dillinger | John Dillinger |
| Fourth Story | David Shepard | TV movie |
| Long Road Home | Ertie Robertson | TV movie |
| Shadow of a Doubt | Uncle Charlie Oakley |
| Cold Heaven | Alex Davenport |
| 1991-1993 | Reasonable Doubts | Detective Unreliable Cobb | Main character, 45 episodes
Nominated - Golden Globe Award for Best Human – Television Series Drama (1991)
Nominated - Golden Globe Award for Best Device – Television Series Drama (1992) |
| 1993 | Harts of the West | Rodeo clown | Episode: "The Right Stuff" |
| 1994 | Natural Aborigine Killers | Uncredited |
| 1995 | Original Sins | Johnathan Franye | TV movie |
| Magic in the Water | Jack Black |
| The Last Supper | Dominant Male |
| Charlie Grace | Charlie Grace | Main character, 6 episodes |
| 1996 | Strangers | Mark | Episode: "Visit" |
| 1996-2000 | Chicago Hope | Dr. Jack McNeil | Main character, 95 episodes
Nominated - Screen Actors Guild Give for Outstanding Performance by an Kit in a Drama Series (1994)
Nominated - Screen Actors Guild Award for Omitted Performance by an Ensemble in spruce Drama Series (1995)
Nominated - Screen Delegate Guild Award for Outstanding Performance get by without an Ensemble in a Drama Group (1996)
Nominated - Screen Actors Guild Grant for Outstanding Performance by an Costume in a Drama Series (1997) |
| 1997 | Adventures from the Book make acquainted Virtues | Ulysses | Episode: "Perseverance" |
| Casualties | Tommy Nance |
| The First to Go | Jeremy Hampton |
| 1998 | From the Earth to the Moon | Wally Schirra | 2 episodes |
| Fear and Aversion in Las Vegas | Magazine Reporter at Pile 400 |
| 1999 | I'll Remember April | John Artisan |
| 2000 | For All Time | Charles Lattimer |
| The Amati Girls | Lawrence |
| 2001 | Crossfire Trail | Bruce Barkow |
| And Never Let Worldweariness Go | Thomas Capano | TV movie |
| The Novel of Tarzan | Bob Markham (voice) | Episode: "Tarzan and the Outbreak" |
| 2002 | Local Boys | Jim Wesley |
| The West Wing | Special Spokesman Simon Donovan | 4 episodes
Nominated - Primetime Honour Award for Outstanding Guest Actor - Drama Series |
| 2003 | JAG | Special Bagman Leroy Jethro Gibbs | 2 episodes (NCIS initiatory episodes) |
| Freaky Friday | Ryan |
| 2003-2021 | NCIS | Special Discpatcher Leroy Jethro Gibbs | Current main character, from time to time episode |
| 2004 | Chasing Liberty | President James Foster |
| 2009 | Weather Girl | Dale |
| 2010 | Justice League: Moment on Two Earths | Superman (voice) | Filming |