| Year | Title | Role | Notes |
| 1955 | The Vise | Tony Mason | 1 episode ("Gift from Heaven") |
| 1958 | The Vise | Vance | 1 episode ("Blood in the Sky") |
| 1958 | Armchair Theatre | Jack 'Pal' Smurch | 1 episode ("The Greatest Man in the World") |
| 1959 | Brand | Priest Brand | Henrik Ibsen play |
| 1961 | Armchair Theatre | Nicholai Soloviov | 1 episode ("The Man Out There") |
| 1960–62 1964–67 | Danger Man | John Drake | 39 + 47 episodes. Also directed three episodes. |
| 1963 | Walt Disney's Wonderful World of Color | Doctor Christopher Syn/ Scarecrow of Romney Marsh | 3 episodes |
| 1967–68 | The Prisoner | Number Six | 17 episodes. Also directed five episodes. |
| 1969 | Journey into Darkness | Host | Made-for-TV film |
| 1974 | Columbo | Colonel Lyle C. Rumford | 1 episode ("By Dawn's Early Light") |
| 1975 | Columbo | Nelson Brenner | 1 episode ("Identity Crisis"). Also directed. |
| 1976 | Columbo | N/A | 1 episode ("Last Salute to the Commodore") – director |
| 1977 | Rafferty | Doctor Sid Rafferty | 13 episodes. Also directed one episode. |
| 1979 | The Hard Way | John Connor | Made-for-TV film |
| 1983 | Jamaica Inn | Joss Merlyn | - |
| 1985 | American Playhouse | Chief magistrate | 3 episodes ("Three Sovereigns for Sarah" parts I, II & III) |
| 1987 | Murder, She Wrote | Oliver Quayle | 1 episode ("Witness for the Defense") |
| 1990 | Columbo | Oscar Finch | 1 episode ("Agenda for Murder"). Also directed. |
| 1998 | Columbo | Eric Prince | "Ashes to Ashes". Also directed. |
| 2000 | Columbo | N/A | 1 episode ("Murder with Too Many Notes") – director |
| 2000 | The Simpsons | Number Six | 1 episode ("The Computer Wore Menace Shoes") |