Born in England in 1970 Walker's interest in photographs began at the Condé Nast library in London, where he worked on the Cecil Beaton archive before taking up a place at Exeter College of Art to study photography. After graduating, he became assistant to Richard Avedon in New York before returning to England, where he initially concentrated on portrait and documentary work for UK newspapers.
 
At the age of twenty-five, he shot his first fashion story for Vogue, and has photographed for the British, Italian and American editions ever since. He has and continues to contribute to Harper's Bazaar, W, i-D and Vanity Fair magazines, and has worked on advertising campaigns for brands such as Yohji Yamamoto, Guerlain and Dior Parfums. His first major show was held at the Design Museum in London in 2008, coinciding with the publication of his first monograph Pictures. In November 2008, Walker received the Isabella Blow Award for Fashion Creator from The British Fashion Council and, in May 2009, he received an Infinity Award from the International Center of Photography, New York, in recognition for his work as a fashion photographer. In 2012, Walker opened a major mid-career retrospective at Somerset House in London. This incredible exhibition also marked the launch of his second book Story Teller, published by Thames and Hudson. Walker's latest major retrospective, Wonderful Things, opened at the Victoria and Albert Museum in 2019, and will be opening at the J. Paul Getty Museum in May 2023. 
 
Walker's work is held in the permanent collections two of London's most prestigious institutions, the Victoria and Albert Museum and the National Portrait Gallery. More recently, the J. Paul Getty Museum in Los Angeles have acquired several works for their collection.