Marcus became an actor in 1984 after three years of training at Arts Educational Schools in London; he spent the first six months of his career touring throughout London's parks and schools in Robin Hood & The Tree Trick, which was quickly followed by his first film role as Moose in the cult film My Beautiful Laundrette.

In 1996 Marcus's agent arranged a meeting for a small low-budget movie with a then-unknown Director named Guy Ritchie; Ritchie offered Marcus the role of Nick the Greek in Lock, Stock and Two Smoking Barrels alongside Nick Moran, Vinnie Jones, Jason Statham and Matthew Vaughn. Three years later, the film was released and garnered a high level of success.

Marcus played American football in the UK for the BAFL One team Sussex Thunder and retired at the end of the 2007 season. He was interviewed for Sky Sports' Sunday NFL coverage after the Thunder's 2007 fixture at the Ipswich Cardinals. The interview, which was broadcast on 21 October 2007, discussed his acting career, as well as American Football. Marcus has been an offensive line coach at the London Olympians and at Valley Trojans.

In July 2012, Marcus launched a new Gangster London walking tour in association with Brit Movie Tours, in which he explores the dark history of London's East End. He also starred in Perry Bhandal's Interview with a Hitman (2012) as Traffikant, a Romanian Crime Boss, alongside Luke Goss.

In May 2013, Marcus played the roles of Varney, Homeless man, Letting Agent & First Guard in a BBC radio adaptation of Neil Gaiman’s Neverwhere, adapted by Dirk Maggs.

In 2012 Marcus appeared in five feature films: It’s A Lot, Two Days in the Smoke, Gridiron UK, AB Negative and Fast & Furious 6. In April 2012, he completed filming for independent British gangster thriller Two Days in the Smoke, in which he played the hitman Ben, alongside Snatch star Alan Ford and Matt Di Angelo from BBC Hustle. Smoke Director Ben Pickering cast him as the vengeful Max in his second feature, the British psychological thriller Welcome to Curiosity, due for release on 25 May 2018 in the USA and Canada.