Philip Anthony Treacy OBE (born 26 May 1967) is an Irish haute couture milliner, or hat designer,^[a] who has been mostly based in London for his career, and who was described by Vogue magazine as "perhaps the greatest living milliner". In 2000, Treacy became the first milliner in eighty years to be invited to exhibit at the Paris haute couture fashion shows. He has won British Accessory Designer of the Year at the British Fashion Awards five times, and has received public honours in both Britain and Ireland. His designs have been displayed at the Victoria and Albert Museum and the Metropolitan Museum of Art.

In 1989, Treacy was discovered and then mentored by fashion editor Isabella Blow, whom Treacy described as the "biggest inspiration" on his life. Blow would wear and promote Treacy's designs at important fashion events and helped Treacy to break into some of the main fashion houses, particularly Chanel and Givenchy. Treacy is associated with celebrities such as Lady Gaga, Madonna, and Sarah Jessica Parker. He has been associated with British royalty and has designed hats for royal occasions, including the fascinator (or "pretzel hat") worn by Princess Beatrice in 2011.