Magrs was born in Jarrow, Tyne and Wear on 12 November 1969. In 1975, he moved with his family to Newton Aycliffe, County Durham; his parents divorced shortly after the move. At the age of 17, Magrs was queer-bashed, and his father was the police officer who took the report on the incident; it was the last time Paul Magrs saw his father.
In Newton Aycliffe, Magrs attended Woodham Comprehensive School, where Mark Gatiss was two years ahead of him and in the same drama group. Magrs went on to Lancaster University, where he received a first class BA in English (1991), an MA in Creative Writing (1991) and a PhD in English (1995). His doctoral thesis was on Angela Carter regarded as a Queer writer.
Magrs is the author of numerous fiction and non-fiction works. His first published writing was the short story "Patient Iris", published 1995 in New Writing Four (edited by A. S. Byatt and Alan Hollinghurst). This was soon followed by his debut novel, Marked for Life, the same year. Magrs' first three novels, Marked for Life, Does It Show? (1997) and Could It Be Magic? (1998), share characters, a magical realist tone and a setting: the fictional Phoenix Court council estate in Newton Aycliffe.
Magrs' first children's book, Strange Boy (2002), prompted controversy due to homosexual content involving its 10-year-old protagonist and a 14-year-old neighbour. Representatives of the NASUWT teachers' union and the conservative Christian Institute argued that the book should not be stocked in school libraries, and some newspapers suggested that doing so in England would be illegal due to the Section 28 ban on "promoting homosexuality" in schools. However, the Chartered Institute of Library and Information Professionals supported libraries' purchase of Strange Boy, as did representatives of Stonewall and other gay rights organizations. Magrs noted that the book was "about 95% autobiographical" and described the controversy as "ludicrous".
Magrs' other novels include Aisles (2003) and To the Devil ... a Diva! (2004); he has also published several short stories. His novel Exchange was shortlisted for the 2006 Booktrust Teenage Prize and was longlisted for the 2007 Carnegie Medal.
Magrs has written several novels, short stories and audio dramas relating to Doctor Who, many of which also feature his character Iris Wildthyme. Iris is generally portrayed as an eccentric and unreliable Time Lady, whose TARDIS takes the form of a London Routemaster double-decker bus (the No. 22 to Putney Common). Iris Wildthyme was originally created for Magrs' unpublished first novel, which was named after her; another version of Iris also appears in Marked for Life. The character features in all of Magrs' four contributions to BBC Books' Eighth Doctor Adventures, in several Big Finish Productions audio dramas by Magrs and other writers, and in short story and novella collections published by Big Finish and Obverse Books. Magrs has also written licensed Doctor Who fiction without Wildthyme, including the 2007 novel Sick Building (which made the shortlist for the Doncaster Book Award) and the audio series Hornets' Nest, which marked the first time Tom Baker had returned to play the Doctor in a full-length drama since he left the role in 1981.
Magrs' current novel series is The Adventures of Brenda and Effie, starring Brenda, the Bride of Frankenstein, who has now retired and runs a B&B in Whitby. She and her friend Effie, a local white witch, investigate spooky goings on in the town. , there have been four books in the series; a fifth, The Bride That Time Forgot, is due for publication in October. The fourth book, Hell's Belles, features characters from Magrs' early Phoenix Court books.
Magrs is Senior Lecturer in English Literature and Creative Writing at Manchester Metropolitan University, where he began work in 2004, having formerly taught at the University of East Anglia. With Julia Bell, Magrs edited several issues of the University of East Anglia's literary journal Pretext and The Creative Writing Coursebook (2001).