Mafham trained at the Bristol Old Vic Theatre School and began his career at the Royal Shakespeare Company, where he spent four years working with directors such as Peter Hall, Danny Boyle, Roger Michell and Max Stafford-Clark.

On television he played Mortimer Lightwood in the BBC's celebrated 'Our Mutual Friend'; Nigel Hawthorn's emotionally scarred son in the multi award winning 'The Fragile Heart'; the dissolute, dark and charming Simon Kingdom, Stephen Fry's errant brother in the hit ITV series 'Kingdom' and the dangerous, ruthless and womanizing Dan Woodhouse in the multi award winning prime time series 'The Clinic'.

In films, Mafham is to be seen playing leading roles in Universal Picture's 'Dragonheart 3' with Ben Kingsley; the Norwegian film 'The Heart of Lightness' based on Ibsen's 'Lady from the Sea'; and Sony Picture's 'Sniper 5, Legacy' with Tom Berenger.