Born in Ahascragh,on the 26th of May 1967 in the West of Ireland, he lived with his parents, seven brothers and one sister across the road from the village church. He moved to Dublin in 1985 to study fashion at the National College of Art & Design, where he made hats “as a hobby” to go with outfits he designed.
In 1988 he won a place on the MA fashion design course at the Royal College of Art in London, and in 1989 he took one of his hats to Michael Roberts, fashion editor of Tatler magazine, and his style editor, Isabella Blow.
In 1990 Treacy graduated from the Royal College of Art with first class honours and set up a workshop in the basement of Isabella and Detmar Blow's house on Elizabeth Street, Belgravia.
He has designed hats for Alexander McQueen's white Haute Couture collection at Givenchy in Paris, for Karl Lagerfeld at Chanel, and for Valentino, Ralph Lauren and Donna Karan. He was awarded the title of British Accessory Designer of the Year at the British Fashion Awards on five occasions during the early 1990s. The late Isabella Blow, style editor of Tatler, helped Treacy launch himself as a well known milliner and wore many of his hats.
He has designed hats for various films including some or all of the Harry Potter films as well Sarah Jessica Parker's hat for the film première of Sex and the City. 36 of Treacy's hats were worn at the wedding of Prince William and Catherine Middleton on 29 April 2011, including the fascinator worn by Princess Beatrice of York.
- Paula Reed; Meredith Etherington-Smith (2001). Philip Treacy. Charta, 2001. p. 72. ISBN 978-88-8158-355-3. Retrieved 11 December 2010.
- Lucia van der Post (2008). Things I Wish My Mother Had Told Me: A Guide to Living with Impeccable Grace and Style. Da Capo Press. p. 56. ISBN 978-0-7382-1278-4. Retrieved 11 December 2010. ""Philip Treacy, generally acknowledged to be Britain's greatest milliner...."
- "Philip Treacy 'Hatforms' at IMMA Thursday". Raidió Teilifís Éireann. 5 April 2001. Retrieved 11 December 2010.
- Roberts, Glenys (9 May 2007). "Isabella Blow: Eccentric to the end". Daily Mail. Retrieved 11 December 2010.
- Susan d’Arcy (19 February 2006). "The g Hotel, Galway". The Times. Retrieved 11 December 2010.
- "Lady Gaga's telephone hat".
- Philip Treacy: King of Royal wedding hats Irish Independent, 2011-04-29
- Newscore (11 May 2011). Princess Beatrice's ridiculed wedding hat to be sold on eBay New York Post