At school his art teacher encouraged him having seen his talent. Art remained his strong subject through school years, and it was a natural progression that Ellison then moved on to art college, firstly at Wimbledon and then Camberwell.
He worked in the merchant navy, trained as a graphic designer and worked as a minicab driver. His first drama job was assistant stage manager at the Richmond Theatre. His first acting role was in the play Woman in a Dressing Gown at said theatre. His first break was a guest appearance in The Sweeney (1975).
He appeared in many guest roles in TV shows throughout the 1970s, including episodes of The Sweeney and The Professionals, and in the films Rosie Dixon - Night Nurse (1978), Lady Oscar (1979), and Buster (1988), based on the Great Train Robbery of 1963.
In 1984, he appeared in Paul McCartney's feature film Give My Regards To Broad Street playing Rath's Minder. In 1986, he played criminal gang leader Charlie Elkin in Running Scared, based on Bernard Ashley's novel.
Having first appeared as Detective Sergeant Burnside in 1984, he became a regular cast member of The Bill from 1988 to 1993 with Burnside now a Detective Inspector. After an absence of 5 years, Burnside returned on a semi-regular basis from 1998 to 2000 having been promoted to the rank of Detective Chief Inspector during the interim.
He appeared in one episode of the sci-fi police series, Crime Traveller, in 1997.
Although best known for playing tough guys, he also played George, a transvestite, in the radio series The Change from 2001 to 2004.
In 2003, Ellison played the lead role in Fort Boyard, which aired on Challenge. In 2005, he guest starred in the Doctor Who audio adventure The Game. In 2007, Ellison played the role of Len Harker in the BBC One soap opera, EastEnders.
He has appeared in Casualty, Judge John Deed, and Minder, among other appearances on Soccer AM, and presenting roles in The World's Most Stupid Criminals and Mousetrapped.
In February 2009, Ellison won Celebrity Come Dine with Me on Channel 4. In 2009, he appeared in the film A Silent Whistle and in 2010 Bonded by Blood and Basement.
In August 2011, he appeared in a New Tricks episode titled 'Half Life' as a prisoner. On 27 August 2015, he entered the Celebrity Big Brother house. He was evicted on 8 September 2015.
In 2017 he appeared on the celebrity version of the television game show Pointless.