Marshall made an early career appearance on the police series
The Bill but it was in 2000 that his major breakthrough role came as
Nick Harper in the
BBC sitcom My Family. In 2003, he appeared in the film
Love Actually as Colin Frissell, an
Englishman who goes to
Milwaukee, Wisconsin to find love. In 2004, Marshall appeared as DS Luke Stone in the police drama series
Murder City. From 2005 to 2011, Marshall appeared on TV and in print for
BT Retail adverts, where he played the character Adam; with
Esther Hall portraying his character's eventual wife Jane. He also played The Ginger Dave in the BBC comedy series
Citizen Khan in 2012 but left after season 1. Since departing his full-time role in
My Family in 2003, Marshall made guest appearances three times appearing in 2 episodes of season five in 2004 and his final appearance in a short
Comic Relief special in 2005. He finished working on the film
Heist at the end of 2006, which aired in April 2008 on
BBC Four. During the summer of 2008, Marshall appeared at
Trafalgar Studios in the first UK run of
Neil LaBute's play
Fat Pig. He became a regular cast-member, playing the character of Ethan on the series
Traffic Light in 2011. In April 2013, it was announced that Marshall would be joining the cast of BBC drama
Death in Paradise as the island's new lead detective, DI
Humphrey Goodman. His character was introduced in the first episode of the third series which aired in 2014, with his first case being to solve the murder of his predecessor, DI Richard Poole (played by
Ben Miller). In January 2017 it was leaked that Marshall would be leaving the series citing the pressures it placed upon his family and that he would be replaced by
Ardal O'Hanlon who plays DI Jack Mooney. Marshall starred as Tom Sanger in the 2015 independent British romantic comedy
Sparks and Embers. Marshall reprised the role of DI Humphrey Goodman from
Death in Paradise in a BBC spin-off
Beyond Paradise, set in South
Devon, which first aired in February 2023. ==Personal life==