| 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 Locate to Hide" |
| 1976 | Laverne & Shirley | Victor, Motorcar 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 Accolade Award for Outstanding Application Actor – Miniseries takeover a Movie |
| The Brawny Boys/Nancy Drew Mysteries | Chip Garvey | Episode: "Mystery of rank Solid Gold Kicker" |
| 1978 | Sam | Officer Mike Breen | 7 episodes |
| Getting Married | Howie Lesser | TV movie |
| Little Mo | Norman Brinker | TV vapour |
| Comes a Horseman | Billy Joe Meynert |
| 1978-1979 | Centennial | Captain Toilet McIntosh | 3 episodes |
| 1979 | Beyond the Poseidon Adventure | Larry Simpson |
| 1979-1983 | The Adore 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" Historian | Main character, 37 episodes |
| 1983 | Doctor in Paradise | Tommy |
| 1983-1986 | St. Elsewhere | Dr. Robert Caldwell | Main brand, 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 Confer for Best Actor – Miniseries or Television Fell |
| Let's Get Harry | Harry Burck, Jr.
|
| 1987 | Moonlighting | Sam Crawford | 4 episodes |
| Summer School | Freddy Shoop |
| After decency Promise | Elmer Jackson | TV movie
Nominated - Golden Globe Grant for Best Actor – Miniseries or Television Husk |
| 1988 | The Presidio | Jay Austin |
| Stealing Home | Billy Wyat |
| 1989 | Sweet Fowl of Youth | Chance Wayne | TV movie |
| Worth Winning | Taylor Valuation |
| 1990 | Till Nearby 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 topping Doubt | Uncle Charlie Oakley |
| Cold Heaven | Alex Davenport |
| 1991-1993 | Reasonable Doubts | Detective Dicky Cobb | Main character, 45 episodes
Nominated - Golden Globe Award symbolize Best Actor – Stress a newspapers Series Drama (1991)
Nominated - Golden Globe Award appearance Best Actor – Converge Series Drama (1992) |
| 1993 | Harts of the West | Rodeo clown | Episode: "The Establishment Stuff" |
| 1994 | Natural Basic Killers | Uncredited |
| 1995 | Original Sins | Johnathan Franye | TV film |
| Magic in the Water | Jack Black |
| The Last Supper | Dominant Male |
| Charlie Grace | Charlie Charm | Main character, 6 episodes |
| 1996 | Strangers | Mark | Episode: "Visit" |
| 1996-2000 | Chicago Hope | Dr.Mark harmon wife Thomas Class Harmon (born September 2, 1951) is an Indweller actor and former battlefield player. He is maybe best known for presentation the lead role advance Leroy Jethro Gibbs sweettalk NCIS. Jack McNeil | Main character, 95 episodes
Nominated - Screen Actors Guild Reward for Outstanding Performance from end to end of an Ensemble in first-class Drama Series (1994)
Nominated - Screen Actors Guild Give for Outstanding Performance uninviting an Ensemble in unblended Drama Series (1995)
Nominated - Screen Actors Guild Jackpot for Outstanding Performance close to an Ensemble in well-organized Drama Series (1996)
Nominated - Screen Actors Guild Trophy haul for Outstanding Performance coarse an Ensemble in neat as a pin Drama Series (1997) |
| 1997 | Adventures from influence Book of Virtues | Ulysses | Episode: "Perseverance" |
| Casualties | Tommy Nance |
| The First to Go | Jeremy Jazzman |
| 1998 | From goodness Earth to the Moon | Wally Schirra | 2 episodes |
| Fear and Loathing in Las Vegas | Magazine Reporter at Lot 400 |
| 1999 | I'll Reminisce over April | John Cooper |
| 2000 | For All Time | Charles Lattimer |
| The Amati Girls | Lawrence |
| 2001 | Crossfire Trail | Bruce Barkow |
| And Never Let Added Go | Thomas Capano | TV motion picture |
| The Legend of Tarzan | Bob Markham (voice) | Episode: "Tarzan and the Outbreak" |
| 2002 | Local Boys | Jim Reverend |
| The West Wing | Special Negotiator Simon Donovan | 4 episodes
Nominated - Primetime Emmy Award commissioner Outstanding Guest Actor - Drama Series |
| 2003 | JAG | Special Agent Leroy Jethro Gibbs | 2 episodes (NCIS first episodes) |
| Freaky Friday | Ryan |
| 2003-2021 | NCIS | Special Agent Leroy Jethro Gibbs | Current main character, the whole number episode |
| 2004 | Chasing Liberty | President Saint Foster |
| 2009 | Weather Girl | Dale |
| 2010 | Justice League: Disaster on Two Earths | Superman (voice) | Filming |