Bowles started his career with the Old Vic Company in 1956 playing small parts in Macbeth, Romeo and Juliet, Troilus and Cressida and Richard II. After a season this company toured North America, concluding with a sell-out season at the Winter Garden Theatre on Broadway. He played in many performances at the Bristol Old Vic.

Bowles has also featured in many films in his long career, including Live Now, Pay Later (1962), The Informers (1963), Three Hats for Lisa (1965), Michelangelo Antonioni's Blowup (1966), The Charge of the Light Brigade (1968), Laughter in the Dark (1969), Eyewitness (1970), Taste of Excitement (1970), A Day in the Death of Joe Egg (1972), The Offence (1972), Endless Night (1972), The Legend of Hell House (1973), For the Love of Benji (1977), The Disappearance (1977), Try This One for Size (1989), The Steal (1995), Colour Me Kubrick (2005), The Bank Job (2008), and Alan in Hong Khaou's Lilting (2014) with Ben Whishaw and Cheng Pei-pei.

His next play was Alan Ayckbourn's Absent Friends, also starring Richard Briers, at the Garrick Theatre in 1975. Then came Tom Stoppard’s Dirty Linen and New-Found-Land at the Arts Theatre in 1976. (Bowles had last played there in 1963 in Anthony Powell's Afternoon Men in a cast that also included James Fox, Alan Howard and the Actress and pop Artist Pauline Boty).

Bowles' first starring role in the theatre after many years of TV successes was as Archie Rice in John Osborne's The Entertainer at the Shaftesbury Theatre in 1986; he was the first actor to play the part in London since Laurence Olivier in 1957.

In 1990 Bowles starred opposite Sir Michael Gambon in Alan Ayckbourn's Man of the Moment at the Globe Theatre.

In 1991 Bowles took an idea for a dramatic film to the BBC; it was accepted, and after being written and adapted by Simon Gray, became the highly regarded Running Late episode of Screen One. This was to be Bowles' first performance on BBC TV since To the Manor Born fifteen years earlier. Bowles, besides starring, also co-produced with Verity Lambert. The film went on to win The Golden Gate Award in 1993 at the San Francisco International Film Festival and in 2013 was shown to great acclaim at the British Film Institute in London.

Bowles' final villainous role, on television at least, was playing Balor ('the most evil man in the universe') in an episode of Space: 1999. He also appeared as Caractacus in the TV adaptation of I, Claudius (1976). His first major English role was Guthrie Featherstone QC MP, whom he played in many series of Rumpole of the Bailey (1978–1992), whilst in 1975 he played David Grant, husband of Abby Grant in the BBC series Survivors. (This came as a surprise to many as at this time, he was a fairly well known personality and in Survivors, he died in the first episode.)

In 2016/17 Bowles played the recurring role of the Duke of Wellington in the award-winning ITV series Victoria.

Bowles played the ultimate gangster in Mellis and Scinto’s Gangster No 1 at the Almeida Theatre in 1995 for which he held the film rights; he raised money from Channel 4 Films and was executive Producer for the 2000 cult film Gangster No. 1, starring Paul Bettany.