English stage and screen actor, latterly noted for his role as Targaryan loyalist Grand Maester Mellos in HBO's epic series House of the Dragon (2022). The son of child care worker Morris Horovitch and his wife Alice (a teacher), he was born in London, schooled in Hertfordshire and trained for acting at the Central School of Speech and Drama. Horovitch made his theatrical debut in Saint Joan at the Everyman Theatre in Cheltenham in 1966. Between 1982 and 2004, he acted in plays for the Royal Exchange in Manchester, where his roles included Prospero in The Tempest and Torvald Helmer in Ibsen's A Doll's House. On screen from 1970, he became best known as Detective Inspector Slack, an amateur conjurer and acquaintance of Miss Marple, in five BBC adaptations of the Agatha Christie mysteries, beginning with Miss Marple: The Body in the Library (1984). He also portrayed Commander Daniels, a murder suspect, in the Poirot (1989) episode The Kidnapped Prime Minister.

In the early 80's, Horovitch starred in the relatively obscure TV series Bognor (1981) as a special investigator for the Board of Trade. The show consisted of twenty-one half hour episodes. It was axed after two seasons, following a regime change at Thames Television. Horovitch has featured in many other crime/action series, including The New Avengers (1976), The Sandbaggers (1978), Bulman (1985), A Touch of Frost (1992) and Foyle's War (2002), as well as in period drama and literary adaptations (eg. the Queen's physician Sir James Clark in The Young Victoria (2009); the dissolute, debt-ridden Reverend Bute Crawley in Vanity Fair (1987); Miss Haversham's cousin Matthew Pocket in Great Expectations (1999)). He has been more recently cast as personae of senior rank or status, including as a German World War II Vice Admiral in The Man with the Iron Heart (2017) and as Cardinal Conroy, who dispatches the heroic Sister Irene on her demon-killing mission in The Nun (2018) (and its sequel).

Horovitch has also recorded a number of audio books, including Joseph Conrad's The Secret Agent and poetry readings of Wordsworth and Shelley.