Born near Paris in 1943 to a modest family, he spent his childhood in Le Havre with his mother and four brothers. For his seventeenth birthday, his stepfather bought him his first Eastman Kodak camera. Demarchelier learned how to develop film, retouch negatives and began shooting friends and weddings.

In 1975, he left Paris for New York to follow his girlfriend. He discovered fashion photography by working as a freelance photographer and learning and working with photographers such as Henri Cartier-Bresson, Terry King, and Jacque Guilbert. His work drew the attention of Elle, Marie Claire and 20 Ans Magazine.

Demarchelier has shot international advertising campaigns for Dior, Louis Vuitton, Celine, TAG Heuer, Chanel, Yves Saint Laurent, Lacoste, Calvin Klein and Ralph Lauren.