Keating was born in Leicester to an Irish father and an English mother; his grandfather, a brigadier, was awarded an OBE from King George VI. His first stage performance was in primary school, playing a cripple in The Ragged School. He then attended Uppingham School.

After graduating from the University of London with a B.A. in History, he tried various jobs before deciding to be a professional actor. To obtain his Equity card, Keating worked in a drag act called Feeling Mutual.

As of 2005, Keating maintains homes in both London and Los Angeles. He enjoys golfing, swimming, music, boogie boarding, tennis, reading and traveling.

Keating had success on the UK stage prior to working as a television and film actor. He originated the role of "Cosmo" in Philip Ridley's The Pitchfork Disney, as well as that of "Bryan" in Michael Wall's Amongst Barbarians, for which he won a Mobil Award. He has since done additional stage work in both the UK and in Los Angeles.

Keating first came to major public attention in the UK when he had a semi-regular role in the Channel 4 sitcom Desmond's (1989-95), the first sitcom to feature a nearly all-black cast. He went on from this to a role in Inspector Morse, as well as other guest-starring roles.

Having moved to the United States, he gained the role of the demonic warrior Mallos on the short-lived series, The Immortal. He starred in the Zalman King series chromiumblue.com. He also made guest appearances on Buffy The Vampire Slayer,G vs E and Special Unit 2 as well as on several other series prior to a major role on the Star Trek series Star Trek: Enterprise, where he played Lieutenant Malcolm Reed. Since then he has had a guest role on the series Las Vegas.

Keating will join the cast of hit show Heroes for its upcoming second season and will play an Irish mobster with special powers, as reported by Variety.

He has appeared in films, including The Hollywood Sign, Jungle 2 Jungle, The Auteur Theory and the upcoming films Certifiably Jonathan, Hollywood Kills, and Robert Zemeckis' animated version of Beowulf. At a Star Trek convention in Sacramento, California on September 9, 2006, he announced that he had just been cast as an Australian scientist in the Species sequel Species IV. He has also recently done work in several short films, including the latest by Tim Russ, called Plugged, a satire on modern advertising. The film is currently in final edits.

Keating also does commercial and voiceover work, perhaps most famously on an early 1990s Vidal Sassoon commercial, where his pronunciation of "salon" and dashing good looks brought him some notice as well as a spoof on Saturday Night Live. He has also done voice work for various audio books. He's recently created quite a stir with his work as Ian Westbury, as part of a Sprint/Nextel campaign for a new phone.