Jonathan Newth is a British actor who has appeared extensively in British television drama for over 50 years. Newth trained at the Central School of Speech and Drama. Newth's theatre work includes appearances with the RSC, in the West End and on Broadway. Newth's television credits include Emergency Ward 10, The Six Wives of Henry VIII, Ace of Wands, The Troubleshooters, Z-Cars, Callan, Van der Valk, The Brothers, Softly, Softly, Poldark, Doctor Who (Underworld), Notorious Woman, Secret Army (Barsacq), The Professionals, The Nightmare Man, The Day of the Triffids, Tenko (Colonel Clifford Jefferson), Triangle, Angels, Juliet Bravo, After Henry, The Adventures of Sherlock Holmes ("The Bruce-Partington Plans"), Boon, Bugs, The Bill, Agatha Christie's Poirot (Dumb Witness), Peak Practice and Heartbeat.
| Series | The Crown | Page (Buckingham Palace) | 2016-11-04 |
| Series | The Lost Honour of Christopher Jefferies | Geoffrey | 2014-12-10 |
| Movie | Remembering Douglas Camfield | 2013-09-30 | |
| Movie | Into the Unknown | 2010-03-29 | |
| Movie | The Affair of the Necklace | Magistrate de Marce | 2001-11-30 |
| Movie | Incognito | Judge | 1997-11-14 |
| Series | Peak Practice | Sir Malcolm Harvey | 1993-05-10 |
| Series | Heartbeat | Mr Roberts | 1992-04-10 |
| Series | Agatha Christie's Poirot | Dr Grainger | 1989-01-08 |
| Series | After Henry | Russell Bryant | 1988-01-04 |
| Movie | The Fools on the Hill | Mr Piggot-Smythe | 1986-10-27 |
| Series | Casualty | Dr. Elliott | 1986-09-06 |
| Movie | A Voyage Round My Father | Boustead | 1984-04-19 |
| Movie | The Case of Marcel Duchamp | Darriand | 1984-04-08 |
| Movie | Champions | Mr Griffin Jones | 1984-04-20 |
| Series | Sherlock Holmes | Colonel Valentine Walter | 1984-04-24 |
| Movie | Tennis Court | Harry Dowd | 1984-12-17 |
| Series | Hammer House of Mystery and Suspense | Harry | 1984-09-05 |
| Movie | Pope John Paul II | Archbishop Adam Sapieha | 1984-04-22 |
| Movie | The Wire | 1983-09-03 | |
| Movie | Accounts | James | 1983-12-22 |
| Movie | Spider's Web | Henry Hailsham-Brown | 1982-12-26 |
| Series | The Nightmare Man | Colonel Howard | 1981-05-01 |
| Movie | The Nightmare Man | Colonel Howard | 1981-05-01 |
| Series | The Day of the Triffids | Dr Soames | 1981-09-10 |
| Series | Tenko | Brigadier Clifford Jefferson | 1981-10-22 |
| Movie | No Defence | Andrew Pelham | 1980-02-14 |
| Series | Juliet Bravo | Alan Cunningham | 1980-08-30 |
| Movie | North Sea Hijack | Kirk | 1980-02-18 |
| Movie | Doctor Who: Underworld | Orfe | 1978-01-28 |
| Series | An Englishman's Castle | Theo | 1978-06-05 |
| Series | Secret Army | Jean Barsacq | 1977-09-07 |
| Series | The Professionals | James Tibbs | 1977-12-30 |
| Movie | Yellow Dog | Tim | 1973-08-11 |
| Series | Van der Valk | Chemist | 1972-09-13 |
| Series | The Six Wives of Henry VIII | George, Viscount Rochford | 1970-01-01 |
| Series | Play for Today | Andrew Pelham | 1970-10-15 |
| Movie | The Suicide Club | Lt. Brackenbury Rich | 1970-02-09 |
| Series | Callan | Unknown | 1967-07-08 |
| Movie | Carry On Spying | Guard (uncredited) | 1964-06-01 |
| Series | Doctor Who | Orfe | 1963-11-23 |