Marsan was born on 9 June 1968[1] in the Stepney district of London to a working-class family; his father was a lorry driver and his mother was a school dinner lady and teacher's assistant.

[8] His first year at drama school was funded by Mr Benny, a bookmaker who ran a menswear shop where Marsan worked; he obtained scholarships for the rest of the course.

Marsan went on to have roles in Casualty, The Bill, Grass, Kavanagh QC, Grange Hill, Silent Witness, Ultimate Force, Southcliffe,[10] and more.

[11] In 2011, he starred alongside Olivia Colman and Peter Mullan, all three actors relatively unknown at that time, in the British drama film Tyrannosaur.

[19] He was critical of the lack of representation of working-class people in the arts in 2015 on BBC Radio 5 Live in which he stated too much drama is written from "the white, privileged, middle class perspective".