Dewi Humphreys was born in February 1947 at Ysbyty Dewi Sant, Bangor, Gwynedd (sources differ on the exact day, giving either the 4th or the 6th), the eldest child of the celebrated Welsh novelist and poet Emyr Humphreys and his wife Elinor Myfanwy (n'ee Jones). He was educated at St Cyres School in Penarth, where his Welsh-language teacher was the actor Noel Williams, whom Humphreys would later cast in his own directorial debut.
After a year studying Law at Sheffield University, Humphreys left to work in the film industry, starting as a clapper loader and focus puller before rising to camera operator on major productions including 'Quadrophenia', 'Chariots of Fire', 'Pink Floyd – The Wall', 'The Dresser' and the James Bond film 'For Your Eyes Only'.
He moved into directing in 1990 and became one of British television's most prolific comedy directors, working on 'The Vicar of Dibley', 'My Family', 'Absolutely Fabulous', '2point4 Children', 'The Green Green Grass' and 'Still Open All Hours', among many others. He also directed the 1996 mini-series 'Neverwhere', devised by Lenny Henry and Neil Gaiman.
Humphreys' Welsh connection is well established: he was born in Bangor into a Welsh-speaking family, and his younger brother Siôn Humphreys is also a television director and producer.