One of the leading players in British Doctor Who fandom's fan-fiction movement during the 1980s, Topping's first published fiction was the BBC Books "Past Doctor Adventure" The Devil Goblins from Neptune in 1997. The novel was co-written with his friend and frequent collaborator Martin Day.
The pair quickly followed this up with the acclaimed novel The Hollow Men in 1998. Following Day's move into TV scripting, Topping wrote the novels The King of Terror (2000) and Byzantium! (2001) solo. The latter novel is the only BBC Books Past Doctor Adventure to be set entirely within one episode of the television series Doctor Who — 1965's The Romans by Dennis Spooner. Topping also wrote the Telos Doctor Who novella Ghost Ship which was published in 2002 and proved so popular that it was one of only two novellas reissued as a paperback edition in 2003.
As well as writing fiction, Topping has also authored numerous programme guides to television series as diverse as The X Files, The Avengers, Star Trek: The Next Generation, The Sweeney and The Professionals. These were all published by Virgin Books, and co-written with Martin Day and Paul Cornell. Cornell, Day and Topping also collaborated on the popular Doctor Who Discontinuity Guide, published by Virgin Books in 1995 and re-issued, in the US, by MonkeyBrain Books in 2004, a lighthearted guide to the mistakes and incongruities of the television series. The trio had first worked together co-writing two editions of The Guinness Book of Classic British Television (1993 and 1996 respectively).
Subsequently, Topping wrote The Complete Slayer: An Unofficial and Unauthorised Guide to Every Episode of Buffy the Vampire Slayer and a number of related texts on this popular series as well as guide books to The West Wing (Inside Bartlet's White House), Angel (Hollywood Vampire), 24 (A Day in the Life) and Stargate SG-1 (Beyond the Gate), amongst others. According to the 2003 book Slayer Slang by Michael Adams (Oxford University Press), Topping was the originator of the word 'vampiry' (adj. "exhibiting features of a vampire") in the January 2000 edition of his book Slayer (pg. 26). In addition, Topping is a regular contributor of articles and reviews to several TV and genre titles including TV Zone, Xposé and Shivers and is a former Contributing Editor of Dreamwatch. He also worked as Project Consultant on Charmed: The Complete DVD Collection.
On radio, Topping was the Producer/Presenter of the monthly Book Club (2005-2007) and currently co-presents a daily television review slot, Monday to Friday, on The Simon Logan Show for BBC Newcastle. He has also contributed to the BBC television series' I Love the '70s, Call The Cops and The Perfect Detective and has written for Sounds, the Daily Telegraph and The Sunday Times Culture Supplement and many other magazines and periodicals.
Topping writes, and occasionally performs, stand-up comedy and has written radio comedy sketches, an (unproduced) stage play and a TV pilot (with Martin Day) that is, currently, stuck in “Development Hell.”
Topping continues to live and work on Tyneside. He achieved a lifetimes ambition in 2005 when his book on The Beatles, Do You Want to Know a Secret was published by Virgin Books.