Already known in Doctor Who fan circles, Cornell's professional writing career began in 1990 when he was a winner in a young writers’ competition and his entry, Kingdom Come, was produced and screened on BBC Two. Soon after, he wrote Revelation, a novel for the Virgin New Adventures series of Doctor Who novels. Timewyrm: Revelation was a reworking of a serialised fan fiction piece Cornell had penned previously for the fanzine Queen Bat. Several other Doctor Who novels followed, including the award-winning Human Nature.

Cornell then began working for Granada Television, where he wrote for the popular children’s medical drama Children's Ward and created his own children’s series Wavelength for Yorkshire Television, which ran for two series. He made the crossover to working in adult television full-time in 1996, when he was one of the main contributors to Granada’s supernatural soap opera Springhill, which ran for two years on Sky One and later on Channel 4.

After a short stint on Coronation Street, he began working for other production companies, including contributing an episode in 1999 to Red Production Company’s anthology drama series Love in the 21st Century for Channel 4. His episode, entitled Masturbation, starred Ioan Gruffudd as Jack. He was due to be one of the writers on Red Production Company’s planned Queer as Folk spin-off series Misfits, but the series was never made, being abruptly cancelled by Channel 4.

In the 21st century he has written mainly for the BBC, contributing episodes to all three of their regular medical dramas: Casualty, Holby City and the daytime soap opera Doctors. He also contributed to the 1950s-set Sunday evening prime time drama series Born and Bred and was one of the writers of the 2005 series revival of Doctor Who, writing the episode "Father's Day". The episode was nominated for the Hugo Award for Best Dramatic Presentation, Short Form in 2006 and came third in terms of votes for its category. Cornell later wrote a two-part story for Doctor Who's 2007 series, based on his 1995 Virgin New Adventures novel Human Nature. The title of the first episode was also "Human Nature", while the second was titled "The Family of Blood". In 2008, the two episodes were nominated for the Hugo Award for Best Dramatic Presentation, Short Form.

In February 2006, Cornell announced in a post on his weblog Paul Cornell's House of Awkwardness: Robin Hood and business ongoing that he would be writing an episode for the BBC's forthcoming Robin Hood, produced by Tiger Aspect Productions for the same Saturday evening family slot as Doctor Who. He later announced on his blog that he was also writing a second Robin Hood episode for later in the first series. His first episode, "Who Shot the Sheriff?", aired on BBC One on 21 October 2006. His second, "A Thing or Two About Loyalty", followed on 2 December 2006. He also wrote an episode for the second season of another Saturday evening family adventure programme, the ITV science-fiction series Primeval, transmitted in February 2008.

Outside of television, he has been active in various other media, having written six Doctor Who novels for Virgin Publishing and BBC Books during the 1990s, three Doctor Who audio dramas for Big Finish Productions and a fully-animated internet-broadcast Doctor Who adventure, Scream of the Shalka (starring Richard E. Grant as the Doctor) for bbc.co.uk in 2003. He has also written two mainstream science-fiction novels, Something More and British Summertime for Gollancz, and various novels, short stories and audio dramas based around a character he created for the New Adventures, Professor Bernice Summerfield, and whom he later licensed to Big Finish Productions.

He has also co-authored (often working with Keith Topping and Martin Day) several non-fiction books on television, including The Guinness Book of Classic British TV, X-treme Possibilities (a guide to The X-Files), and The Discontinuity Guide (a humorous guide to Doctor Who). (Topping and Day's Doctor Who novel The Devil Goblins from Neptune was also based on an original idea with Cornell.) He has also written comics, both for Doctor Who Magazine and the 2000 AD spin-off Judge Dredd Megazine.

He has written Wisdom, a 6-issue limited series for Marvel Comics' MAX imprint, featuring the character Peter Wisdom, with art by Trevor Hairsine and Manuel Garcia.

It was announced at the 2007 Wizard World Chicago comic book convention that Cornell would be following Chris Claremont on Marvel's New Excalibur. Plans were to subsequently changed with the cancellation of the New Excalibur title and Cornell's new project was announced as being titled 13. The third trade paperback, Vampire State, was nominated for the 2010 "Best Graphic Story" Hugo Award.

Cornell has also written Young Avengers Presents #4 (April 2008) and a Fantastic Four mini-series comic, True Story, which started in July 2008, which will feature the team encountering characters from the pages of literary classics.. In 2008, he wrote a comic which featured on the Doctor Who website. He has also written the Younger Avengers limited series that ties into Dark Reign and Black Widow: Deadly Origin a mini-series that ties into the character's appearance in Iron Man 2.

Cornell has been announced as the next Action Comics writer after War of the Supermen. Cornell signed with DC Comics exclusively in 2010 as part of writing for Action Comics.

He also wrote Pulse, which starts on BBC Three in early June.

In an interview on the DWO Whocast, Cornell stated that this entry in wikipedia described him as "..both a Christian and a pagan..", which he has chosen not to correct as it illustrates his sympathies for the pagan world. He then goes on to state that he is an Anglican but is very "..Low Church, almost a Calvinist.." and this is partly because he doesn't enjoy hymns.

Spiritual themes are not uncommon in his work (for example his novel Something More). Other frequent references in his work include owls. BBC - Doctor Who - Classic Series - Ebooks - Human Nature - Adaptation

Cornell is married to Caroline Symcox, who also has written Doctor Who-based audio plays for Big Finish Productions on her own and with Cornell.

In 2010, he appeared as a contestant on an episode of the BBC 4 quiz show Only Connect.

He has written novels, non-fiction, audio plays and comic scripts.

Novels

Virgin New Adventures

• Doctor Who: Revelation (ISBN 0-426-20360-7)
• Doctor Who: Love and War (ISBN 0-426-20385-2)
• Doctor Who: No Future (ISBN 0-426-20409-3)
• Doctor Who: Human Nature (ISBN 0-426-20443-3)
• Doctor Who: Happy Endings (ISBN 0-426-20470-0)

Virgin Missing Adventures

• Doctor Who: Goth Opera (ISBN 0-426-20418-2)

Eighth Doctor Adventures

• Doctor Who: The Shadows of Avalon (ISBN 0-563-55588-2)

Other Doctor Who novels

• Doctor Who: Scream of the Shalka (ISBN 0-563-48619-8)
• Bernice Summerfield: Oh No It Isn't! (ISBN 0-426-20507-3)
• Bernice Summerfield: The Dead Men Diaries (editor)
• Bernice Summerfield: A Life of Surprises (editor)
• Bernice Summerfield: Life During Wartime (editor)

Other novels

• Something More (ISBN 0-575-07203-2)
• British Summertime (ISBN 0-575-07404-3)
• The Uninvited (ISBN 0-7535-0220-8) (novelisation for Virgin of 1997 ITV science-fiction drama serial)

Non-fiction

• Avengers Dossier: The Definitive Unauthorised Guide (ISBN 0-86369-754-2) with Martin Day and Keith Topping
• Licence Denied: Rumblings from the Doctor Who Underground (ISBN 0-7535-0104-X) (editor)
• X-treme Possibilities: A Paranoid Rummage Through The X-files (ISBN 0-7535-0228-3) with Day and Topping
• The Discontinuity Guide (ISBN 0-426-20442-5) with Day and Topping
• The Guinness Book of Classic British TV with Day and Topping
• The New Trek Programme Guide (ISBN 0-86369-922-7) with Day and Topping

Audio plays

Doctor Who

• The Shadow of the Scourge (2000)
• Seasons of Fear with Caroline Symcox (2002)
• Circular Time with Mike Maddox (2007)

Professor Bernice Summerfield

• Oh No It Isn't! (audio adaptation by Jacqueline Rayner of novel) (1999)
• Death and the Daleks (2004)

Comics

• Doctor Who:
• "Stairway to Heaven" (with co-author John Freeman and pencils by Gerry Dolan and inks by Rex Ward, in Doctor Who Magazine #156, 1990)
• "Teenage Kicks" (illustrated text story, in Doctor Who Magazine #163, 1990)
• "The Chameleon Factor" (with pencils by Lee Sullivan and inks by Mark Farmer, in Doctor Who Magazine #174, 1991)
• "Emperor of the Daleks" (with co-author John Freeman and art by John Ridgway, in Doctor Who Magazine #197-202, 1993)
• "Time and Time Again" (with art by John Ridgway, in Doctor Who Magazine #207, 1993
• "Metamorphosis" (with art by Lee Sullivan, in Doctor Who Yearbook 1993)
• "Blood Invocation" (with art by John Ridgway, in Doctor Who Yearbook 1995)
• Pan-African Judges (with Siku, in Judge Dredd Megazine vol. 2 #44-49, 1993—1994)
• Deathwatch: "Faust & Falsehood" (with Adrian Salmon, in Judge Dredd Megazine vol. 3 #8-13, 1995—1996)
• XTNCT (with D'Israeli, in Judge Dredd Megazine #209-214, 2003—2004, trade paperback, XTNCT: CM ND HV G F Y THNK YR HRD NGH!, 48 pages, hardcover, December 2006, ISBN 1-904265-69-3)
• Wisdom (with Trevor Hairsine and Manuel Garcia, 6-issue limited series, Marvel Comics, 2006, tpb, 144 pages, August 2007, ISBN 0785121234)
• Young Avengers Presents #4 (with Mark Brooks, Marvel Comics, April 2008, collected in Young Avengers Presents, 144 pages, October 2008, ISBN 0785129758)
• 13 #1-15 plus annual (with Leonard Kirk, Marvel Comics, May 2008-July 2009):
• Secret Invasion (collects Captain Britain and MI: 13 #1-4, 104 pages, Panini Comics, January 2009, ISBN 1846534070, Marvel Comics, March 2009, ISBN 0-7851-3344-5)
• Hell Comes To Birmingham (collects Captain Britain and MI: 13 #5-9, 120 pages, Panini Comics, June 2009, ISBN 1846534232, Marvel Comics, July 2009, ISBN 0-7851-3345-3)
• Vampire State (collects Captain Britain and MI: 13 #10-15 + annual #1, 184 pages, Marvel Comics, October 2009, ISBN 0-7851-3952-4)
• Fantastic Four: True Story (with Horacio Dominguez, 4-issue mini-series, Marvel Comics, July-October 2008)
• Dark Reign: Young Avengers (with Mark Brooks, 5-issue limited series, Marvel Comics, May-September 2009)
• Black Widow: Deadly Origin (with Tom Raney and John Paul Leon, 4-issue mini-series, Marvel Comics, forthcoming)
• Dark X-Men: The Beginning #1-3 (with Leonard Kirk, Marvel Comics, September-October 2009, hardcover, December 2009, ISBN 0-7851-4230-4)
• Dark X-Men (with Leonard Kirk, 5-issue limited series, Marvel Comics, January 2010-ongoing, premiere hardcover, June 2010, ISBN 0-7851-4526-5)
• Action Comics #890- (with artist Pete Woods, DC Comics, June 2010-)

Screenplays

Some of the notable series and episodes he has worked on include:

• Doctor Who:
• "Father's Day" (2005)
• "Human Nature" (2007)
• "The Family of Blood" (2007)

• Robin Hood
• "Who Shot the Sheriff?" (2006)
• "A Thing or Two About Loyalty" (2006)

• Pulse (pilot, 2010)

Interviews

• Paul Cornell interviwed at CONvergence 2010 by The Omega Podcast (in mp3 format)
• Podcast Interview with Paul Cornell (in mp3 format)
• Interview with Paul Cornell on the Bullpen Bulletins Podcast
• Interview with Paul Cornell at Millarworld
• Interview with Paul Cornell at YMCA England
• Author interview: Paul Cornell, SFX, June 10, 2008
• Special Edition Podcast: Paul Cornell, iFanboy, July 3, 2008
• X-POSITION: Paul Cornell, Comic Book Resources, September 23, 2008
• Geek Syndicate Podcast Interview with Paul Cornell (in mp3 format)
• Paul Cornell live at BICS 2008 on the Geek Syndicate Panel