After graduating from Oxford University, he joined the BBC's children's department, CBBC, in 1985 on a part-time basis and held various positions, which included creating two series, Dark Season and Century Falls.

Davies was appointed Officer of the Order of the British Empire in 2008 for services to drama, which coincided with the announcement he would step down from Doctor Who as the show's executive producer with his final script, "The End of Time" (2009–2010).

[5] In 1979, Davies completed his O-Levels and stayed at Olchfa with the ambition to study English literature at the University of Oxford; he abandoned his aspirations of becoming a comic artist after a careers advisor convinced him that his colour-blindness would make that path unlikely.

[12] While producing Why Don't You?, Davies branched out within CBBC at BBC Manchester: he attended directors' courses; wrote for older audiences with his contributions to DEF II and On the Waterfront; and accompanied Keith Chegwin to Norway to assist in the production of a children's documentary about politics.

[13] He decided to leave CBBC during the production of Breakfast Serials: a friend called him after the first episode was transmitted and observed he had "broadcast a joke about the juvenilia of Emily Brontë at eight o'clock in the morning"; the conversation caused him to reflect he was writing for the wrong audience.

The next three episodes focus on a new villain: the archaeologist Miss Pendragon (Jacqueline Pearce), later described by Davies as a "devil worshipping Nazi lesbian",[17] who becomes a part of the ancient supercomputer Behemoth.

The series was a tongue-in-cheek deconstruction of organised religion, and featured his first overtly homosexual character: a lesbian vicar portrayed by Sue Holderness, who came out of the closet in a two-hander episode with Carole Nimmons.

The book includes several themes which Davies would intersperse in his later works—including a family called "Tyler" and companion Chris Cwej participating in casual homosexual sex—[27] and a subplot formed the inspiration for The Mother War, a proposed but never produced thriller for Granada about a woman, Eva Jericho, and a calcified foetus in her uterus.

[30] The second series of Springhill continued his penchant for symbolism; in particular, it depicted Marion Freeman (Judy Holt) and Eva as personifications of good and evil, and climaxed with a finale set in an ultra-liberal dystopian future where premarital sex and homosexuality are embraced by the Church.

[33] His scripts for the first series reflect the pessimism of the period; each episode added its own emotional trauma on the staff; these included a soldier's execution for desertion, a destitute maid who threatened to illegally abort her unborn child to survive, and a multi-episode about the chambermaid, Monica Jones (Jane Danson), who kills her rapist in self-defence, is arrested, and eventually hanged for murder.

[35] The second series had a lighter tone and greater emphasis on character development, which Davies attributed to his friend Sally, who had previously warned him of the adult humour in Breakfast Serials; she told him his show was too bleak to be compared to real life.

[42] The series was allocated a £3 million budget, and was produced by Red Productions, owned by his friend and former colleague Nicola Shindler, and filmed by director Charles McDougall and Sarah Hardin on location in Manchester.

[55] To simulate a classic love story, the plot required antagonists, in the form of Bob's best friend and fellow teacher Holly Vance and Rose's boyfriend Andy Lewis (Daniel Ryan).

[57] The subplot climaxes in the fourth episode, when Monica and Bob lead a rally into direct action by handcuffing themselves to a bus run by a company whose management donated millions to keeping the law on the books;[57][58] the scene directly parallels protests against the transport company Stagecoach due to their founder Brian Souter's financial and political support of Section 28—at one point, Davies intended to explicitly name Stagecoach in the script—[58] and is inspired by earlier protests undertaken by the LGBT rights pressure group OutRage!.

The part of Rose was given to Lesley Sharp, her first leading role after her portrayal of secondary characters in past Red shows Playing the Field and Clocking Off, and Jessica Stevenson was cast as Holly by ITV Head of Drama Nick Elliott on the basis of her performance in the Channel 4 comedy Spaced.

The series was the only Red–Davies collaboration not to be scored by future Doctor Who composer Murray Gold;[60] the soundtrack was a Martin Phipps composition inspired by Hans Zimmer's work on the 1993 film True Romance.

[62] Although the series was not as successful as he hoped, the show helped Davies rekindle his relationship with his mother shortly before her death, just after the transmission of the fourth episode, which he sees as "possibly the best thing [he has] ever written".

The series was a departure from his trend of experimental social commentary; it was instead designed to be a mainstream comedy which utilised Welsh actors: Davies and Red Productions even planned a cameo appearance by Academy Award-winning Swansea-born Catherine Zeta-Jones.

[76] The serial takes place primarily during Casanova's early adulthood and depicts his life among three women: his mother (Dervla Kirwan), his lover Henriette (Laura Fraser), and his consort Bellino (Nina Sosanya).

[89] The start of filming created stress among the production team because of unseen circumstances: several scenes from the first block had to be re-shot because the original footage was unusable; the Slitheen prosthetics for "Aliens of London", "World War Three", and "Boom Town" were noticeably different from their computer-generated counterparts; and the BBC came to a gridlock in negotiations with the Terry Nation estate to secure the Daleks for the sixth episode of the series; Davies and episode writer Rob Shearman were forced to rework the script to feature another race, until Gardner was able to secure the rights a month later.

[94] The show began production in April 2006 and was marketed through foreshadowing in the main story arc of Doctor Who's second series, which portrayed Torchwood as a covert quasi-governmental organisation that monitors, exploits, and suppresses the existence of extraterrestrial life and technology.

[100] Dubbed the "Great Correspondence" by Davies and Cook,[101] The Writer's Tale covers a period between February 2007 and March 2008 and explores his writing processes and the development of his scripts for the fourth series of Doctor Who: "Voyage of the Damned", "Partners in Crime", "Midnight", "Turn Left", "The Stolen Earth", and "Journey's End".

[118] He additionally gave informal assistance to and later served as creative consultant of ex-Doctor Who script editor Helen Raynor's and playwright Gary Owen's BBC Cymru Wales drama, Baker Boys.

Davies continued to develop ideas for the show, and explained a pivotal scene in the premiere to Cook in 2007:I can imagine a man who is so enraged by something tiny—the fact that his boyfriend won't learn to swim—that he goes into a rage so great that, in one night, his entire life falls apart.

Davies was convinced to return to the channel by Head of Drama and former Doctor Who executive producer Piers Wenger, who described the show as a "political piece of writing" which creates a "radical approach" to sexuality.

[143] Davies plans to write a series about sextortion, drawing inspiration from real-life incidents of blackmail which resulted in suicide,[144] and to adapt Charles Dickens' The Old Curiosity Shop for television.

[150] For the "Rose" watch party, Davies released a short story originally written in 2013 for the show's fiftieth anniversary—the story was written for Doctor Who Magazine and stylised as the final pages of a Target novelisation, but was not included in the magazine due to continuity conflicts with the anniversary special "The Day of the Doctor";[151] for the "New Earth" and "Gridlock" watch party, he wrote the script for an animated sequel, "The Secret of Novice Hame", with Tennant and Anna Hope reprising their roles as the Doctor and Hame respectively;[152] and for "The Runaway Bride" watch party, Davies shared excerpts of his 1986 spec script, Mind of the Hodiac, which was later optioned by Big Finish for its The Lost Stories audio play range, which was released on 30 March 2022.

[176] He also includes his commentary as an undertone in other stories; he described the sub-plot of the differing belief systems of the Doctor and Queen Victoria in "Tooth and Claw" as a conflict between "Rational Man versus Head of the Church".

[191][192] In 2007, Davies was nominated for the "Best Soap/Series" Writers' Guild of Great Britain Award—along with Chris Chibnall, Paul Cornell, Stephen Greenhorn, Steven Moffat, Helen Raynor, and Gareth Roberts—for their work on the third series of Doctor Who.

[217] Ian Farrington, who commented on the 2009 "Greatest Contribution" poll, attributed Davies' popularity to his range of writing styles, from the epic "Doomsday" to the minimalistic "Midnight", and his ability to market the show to appeal to a wide audience.