He has played Nick Harper in My Family, Colin Frissell in the 2003 film Love Actually, Gratiano in The Merchant of Venice, and Murder City (2006–2008), and Dave in the first series of Citizen Khan (2012).

His father was a Royal Air Force (RAF) navigator, whose career included a posting to the Queen's Flight, eventually becoming a squadron leader.

[2] 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 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.

[5][6] 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).

[7] 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.