Doonan comes from the English town of Reading. His first retail job was a summer position at Heelas, a department store in Reading, now owned by the John Lewis Partnership. After returning to work at the same store after university, he first got involved in the art of window dressing. He later left Reading for London and dressed windows at Aquascutum before moving to Nutters of Savile Row.
Invited to dress his windows by the proprietor of Maxfield, a department store in Los Angeles, Doonan moved to the United States in 1978. He joined the Barneys staff in 1986 as a window dresser.
In his book, Eccentric Glamour, he decried porno chic in Western society in general. Interviewed for an article for the New York Daily News, he said, "There are two horribly worrying trends! Celebrities are becoming so gun-shy that there is no diversity, no sense of fun on the red carpet. There's no experimentation – which is incredibly important to fashion." On "porno chic," (the second trend) he said, "Imagine if you said to people 20 years ago that, in 2008, a significant number of women would be going around dressing like porno stars with fake hooters and butt cracks showing? No one would have believed you."
He has also been a guest star on America's Next Top Model season 2, 3, and 5 to teach the models about style.
In Gossip Girl's fifth season (third episode: "The Jewel of Denial"), he escorted Blair Waldorf on Jenny Packham's show.
Doonan used to dress up as the UK's Queen Elizabeth II, and impersonate her at public appearances, and has written about being born in the same year as Elizabeth's accession to the throne (1952) and his affinity with Elizabeth's pet name, "Brenda".
In January 2013, Doonan made a cameo in an Alexander Wang advertisement. The advertisement takes place in Wang's flagship store in New York, where Doonan is falsely accused by Anjelah Johnson's character Bon Qui Qui for trying to steal a handbag.
- Confessions of a Window Dresser: Tales from the Life of Fashion (2001) ISBN 0-14-100362-6 (Memoir)
- Wacky Chicks: Life Lessons from Fearlessly Inappropriate and Fabulously Eccentric Women (2005) Simon & Schuster ISBN 0-7432-5789-8
- Beautiful People (also published as Nasty: My Family And Other Glamorous Varmints) (2005) ISBN 978-0-00-726954-9
- Eccentric Glamour: Creating an Insanely More Fabulous You (2008) Simon & Schuster ISBN 1-4165-3543-8
- Gay Men Don't Get Fat (2012) Blue Rider Press ISBN 978-0-399-15873-5
- Meet the Most Fashionable Woman in the World: The Queen of England. The Queen's Jubilee: Why she's the most fashionable woman in the world., Simon Doonan, Slate, 15 March 2012, accessed 16 March 2012
- Burton, Laura (25 September 2008). "Fashion should be funny". Guardian News and Media Ltd. Retrieved 10 November 2009.
- Colin Bertram, New York Daily News, 31 March 2008 http://www.nydailynews.com/lifestyle/2008/03/31/2008-03-31_simon_doonan_of_barneys_wants_to_take_us-1.html
- Simon Doonan and Jonathan Adler
- Simon Doonan – TV.com
- Fear of Squat
- Every Expense was Spared
- Jose Garces vs Mike Lata in Iron Chef Battle Sparkling Wine, Raphael Brion, Eater, Monday, 6 December 2010
-  A$AP Rocky and Bon Qui Qui Star in a Hilarious Alexander Wang Ad (Video)