He is best known for his frequent collaborations with Grant Morrison on titles such as New X-Men, We3, All-Star Superman, and Batman and Robin, as well as his work with Mark Millar on The Authority and Jupiter's Legacy.

Deighan was raised in Rutherglen, although attended St. Bride's High School in East Kilbride (as his father worked there as a PE teacher).

[5][6][7] Deighan worked up the Scottish underground comics title Electric Soup in 1990, writing and drawing The Greens, a parody of The Broons strip published by D. C. Thomson.

Initially he worked on strips for anthology titles such as Weird War Tales, and drew three issues of Jamie Delano's 2020 Visions, as well as various covers for DC.

He later drew his first full length graphic novel, Batman: The Scottish Connection, with writer Alan Grant[9] in which The Greens make a cameo appearance.

[11] The graphic novel was met with positive critical response, and later that year Quitely took over from Bryan Hitch as artist on The Authority, with Mark Millar as writer.

[15] He wrote and drew new instalments of The Greens for the Scottish underground comic Northern Lightz,[16] and in 2005 Morrison and Quitely designed a series of tarot cards for Intensive Care, an album by popstar Robbie Williams.

[20] That same year, Quitely again teamed with Morrison, illustrated the first three issues of Batman and Robin title,[21] which debuted in June 2009 after the "Battle for the Cowl" storyline.

With Guinness officials on hand to monitor their progress, writer Mark Millar began work at 9 AM scripting a 20-page black and white Superior comic book, with Quitely and the other artists appearing on stage throughout the day to work on the pencils, inks, and lettering, including Dave Gibbons, John Romita Jr., Jock, Adi Granov,[24] Doug Braithwaite, Ian Churchill, Olivier Coipel, Duncan Fegredo, Simon Furman, David Lafuente, John McCrea, Sean Phillips and Liam Sharp,[25] who all drew a panel each, with regular Superior artist Leinil Yu creating the book's front cover.

[33] Quitely's son Vincent is also an artist who created art for local St Columbkille's RC Church [de] in 2011 while a pupil at Trinity High School.

[36][37] In a 2014 BBC News interview, Deighan, having developed a reputation for difficulty in meeting deadlines, stated while he did his drawing digitally, it did not reduce the time it took to complete his art, saying, "I have never been on a project where I've thought 'ach, this is rubbish', and not tried hard," he says, "It's not in my nature.