In the 1960s, Timothy was part of Laurence Olivier’s National Theatre company and appeared in such productions as The Master Builder, Juno and the Paycock and Olivier’s Othello. Timothy’s television career started with the 1969 series Take Three Girls, and he went on to appear in UFO (1970 episode “The Psychobombs”), Doctor at Large in 1971, Some Mothers Do ‘Ave ‘Em in 1973 and Murder Most English: A Flaxborough Chronicle in 1977 before winning the role of Herriot. He played the role from 1978 until 1990.

In 1980, he played Jesus Christ in the York Mystery Plays. In 2000, he was cast as Mac McGuire in the BBC soap opera Doctors staying in the series for six years, and directing some of the episodes. In 2004, he made an appearance in Casualty as the murderer of long-standing character Finlay Newton. He also appeared as a special guest on ITV1 drama The Bill, which was aired on New Years Day 2009. More recently he has appeared in Lewis (ITV1) in the episode “Wild Justice”, The Grapes of Wrath, All the Fun of the Fair, Haunting Julia and Casualty (2014).

He was the subject of This Is Your Life in 2000 when he was surprised by Michael Aspel on the set of Doctors at the BBC’s Pebble Mill studios in Birmingham.

He is the son of BBC announcer Andrew Timothy, and has done regular voice work himself including taking his father’s place as the Announcer for the Goon Again Show in 2001 marking the 50th anniversary of The Goon Show (Andrew had been the announcer for the show back in the early 1950s). He played the Announcer role on The Kinks’ 1974 double album, Preservation Act 2.

In 2008 Timothy took part in the BBC Wales programme Coming Home about his Welsh family history. In 2011, he played himself in the audio drama We are not the BBC written by Susan Casanove and produced by the Wireless Theatre Company.

He returned to theatre in March 2013 in The Living Room. As of 2014 he is playing Inspector Hubbard in the UK tour of the stage thriller Dial M for Murder.

He voiced and appeared in numerous television commercials for The Sun newspaper in the 1970s (which were extremely unusual for the time in the level of energy and even aggression evident in Timothy’s delivery). In this role he was featured in the 2017 stage production of Ink, played by Jack Holden and directed by Rupert Goold, at the Almeida Theatre, London. He appeared in BBC Radio’s Just a Minute in 1988 and 1989. He was also used in the marketing material for Dignity plc, primarily for their prepaid funeral plans.

In April 2017, it was announced that he would be joining the BBC soap opera EastEnders as regular character Ted Murray, in which he made his last appearance on 27 September 2019. Timothy appeared with Peter Davison in the three-part series Vintage Roads Great & Small in 2018. In it the pair travel in vintage cars on three trips from London to Land’s End, from Loch Ness to The Isle of Skye and from Cardiff to Snowdonia.

In February 2020 Timothy appeared in Shakespeare & Hathaway: Private Investigators as Chamberlain, episode #3.3 “The Sticking Place”.

In April 2020 Timothy appeared in ITV Series Kate & Koji (Series 1, episode 5) When Kate’s flashy ex-husband Dennis arrives in town with his much younger wife, Kate feigns an attachment to Koji