Though he has appeared on stage, winning an Edinburgh Fringe First Award for his show Dead Fish, and in TV bit parts including The Bill and London's Burning, his main fame has come through voiceover work.
Having been taken on as a continuity announcer by Channel 4 in the late 1990s, he was subsequently selected as the narrator of the UK version of Big Brother, which remains his best-known work. He has narrated all nine series to date, as well as the spin-offs Celebrity Big Brother, Teen Big Brother: The Experiment and Big Brother Celebrity Hijack. The producers of Big Brother gave him the job of narrator because they liked the way he said "Chickens". His most notable catchphrase is "Who goes? You decide".
He is one of the UK's most recognisable voiceover artists due to his heavy North-East England "Geordie" accent (which he often exaggerates for effect), and he rarely appears in vision. Besides his many voiceovers, and ongoing continuity work, Bentley was also the unseen questionmaster on a Sky One quiz show, Dirty Money.
Despite having a low-profile he has made a few exceptions. On day 59 of Big Brother 2003 (UK) he was interviewed in the camera run by Dermot O'Leary on BBLB and during Big Brother 2002 (UK) he was interviewed in the studio. On August 13, 2006, to accept his award as Big Brother's Little Brother's employee of the week, the final one of the series. He chose not to appear in person but was interviewed unseen from within the BBLB studio with a voice over Dermot, the host. He made another exception on January 28, 2008, when he made the link to Dermot's best bits while being seated in the Hijacker Booth. His face remained unseen, as all lights were down in the Booth. As part of the running joke surrounding him, Bentley has occasionally been featured on BBLB reading a humorous script for the show, albeit filmed from a back view so as not to reveal what he looks like on the show itself.