Davies () attended Whitchurch Grammar School in Cardiff and then University College, London, where he received a B.A. in English in 1957. He took a teaching position at St. Clement Danes Grammar School in London, where he was on the teaching staff from 1958-61. He held a similar post at Woodberry Down Comprehensive School in Hackney, London from 1961-63. Following that, he was a lecturer in English at Coventry College of Education (which merged with the University of Warwick in 1971 to become the Faculty of Educational Studies and later the Warwick Institute of Education) from 1963-71, and then at the University of Warwick in Coventry from 1971-87.
In 1960, Davies contributed material to the BBC Home Service's Monday Night at Home strand, alongside Harold Pinter and Ivor Cutler. He wrote his first play for radio in 1964. In 1960, he married Diana Huntley; the couple have a son and daughter. He is resident in Kenilworth, a town of Warwickshire.
Davies is the creator of the children's Marmalade Atkins television series and A Very Peculiar Practice, and is also well known for his adaptations of classic works of literature, including the 1995 television adaptation of Pride and Prejudice starring Colin Firth and Jennifer Ehle, the 1998 adaptation of Vanity Fair, and the 2008 BBC adaption of Sense and Sensibility. He is the writer of the screenplays both for the 1994 BBC production Middlemarch and a planned 2009 film of the same name. Middlemarch (2009) Sam Mendes shifts to comedy - Entertainment News, Film News, Media - Variety
Davies also co-devised with Bernadette Davis the laddish sitcom Game On for BBC2 and co-wrote the first two series in 1995 and 1996.
The popularity of his adaptation of Michael Dobbs's political thriller House of Cards was a significant influence in Dobbs's decision to write two sequels, which Davies also adapted for television.
In film, he has collaborated on the screenplays for both of the Bridget Jones films, based on Helen Fielding's successful novels.
His previous career in education he drew upon in writing the campus-based comedy-drama series A Very Peculiar Practice (1986-88).
He is also a prolific writer for children. His works in this field include the Guardian Award-winning Conrad's War, Alfonso Bonzo (book and television series), and the adventures of Marmalade Atkins (television series and numerous books). He also wrote the stories Dark Towers and Badger Girl for the BBC TV Look and Read series of programmes for schools audiences.
2008 saw the release of his adaptations of the 1999 novel Affinity by Sarah Waters, Evelyn Waugh's Brideshead Revisited (a film), Charles Dickens' Little Dorrit (a BBC series). Little Dorrit won 7 out of its 11 Emmy nominations and earned Davies an Emmy for Outstanding Writing for a Miniseries.
Davies' forthcoming projects include a film version of Annie Griffin's Channel 4 situation comedy The Book Group.