Timothy was born in Bala, Merionethshire, Wales and lived in the town up to the age of five, when his parents moved to London. He attended the Priory Grammar School in Shrewsbury in the 1950s, appearing in a number of school plays. On leaving school he worked at Frank Newton's Gentleman's Outfitters in Shrewsbury - now the location of Marks & Spencers in the town. 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. He has also read Herriot's works for CD release.