Marchant, whose father was a printer and mother a school dinner lady, was born and raised on a council estate in Wapping in the East End of London, which he has described as, "a very hard, heavy place to live sometimes.
[4] It was at this point that he ceased pursuing a career in heavyweight professional boxing, although, "getting punched in the face," was, he has claimed, "very good preparation for being a writer.
Looking back on his early career he has stated that at the time he wondered if he were part of, "some sort of liberal social engineering," which advantaged him as an ex-boxer from a council estate with no university education.
In 2008, David Tennant starred in a BBC1 single film, Recovery, in which Marchant explored the aftermath of brain injury on a man's life and family.
This drama centred on the impact the September 11th, 2001 terrorist attacks had on the town of Gander, Newfoundland as hundreds of flights were forced to land outside American airspace.
He wrote episodes for all 3 series of Garrow's Law, the film The Dig and, broadcast in 2012, the hard-hitting drama about the British probation service Public Enemies, all for BBC1.
Marchant received an Honorary Doctor of Letters from the University of Hertfordshire during a ceremony at the Cathedral and Abbey Church of St Alban on November 16, 2011.