Born in Larache, Morocco, Hajjaj moved to the UK with his family when he was 12. Coming of age in London in the 1970s and 80s, the artist worked in fashion, interior design, and clubs, launching his own streetwear label R.A.P in 1984 before such brands became mainstream.
Hajjaj began to show his photographs seriously in the 1990s after a visit to Morocco. In an interview with Vogue in 2020, the artist recalled feeling that Morocco was seen as an exotic backdrop and portrayed without the culture's full vibrancy. In his resultant 'The Arab issue' series, women pose like fashion magazine models while wearing kaftans and jellabiyas that Hassan designed in the polka dots, camouflage, and animal prints that were fashionable at the time.
Hajjaj mounts his photographs in customised frames that are contemporary reinterpretations of traditional Moroccan mosaic and tile motifs. The frames are made out of commercial products including Coca-Cola cans, tires, and cans of food. His use of these materials has attracted comparisons with the Pop art aesthetic of Andy Warhol, while his patterned backdrops acknowledge the work of African photographers like Seydou Keïta, Sanlé Sory, and Malick Sidibé.
Many of Hajjaj's subjects are his close friends and long-time acquaintances, notably Karima, who is a henna artist active in Marrakech and whom he has photographed since 1998. In 'Kesh Angels' (2010), one of his most well-known works, Karima and her friends pose on their motorbikes—the city of Marrakech is known for its biker population—from a lower angle, emphasising their ease and confidence.
In 2009, Hajjaj was shortlisted for the Victoria & Albert Museum’s Jameel Prize for Islamic Art. His solo exhibitions have been held at The Third Line, Dubai; Rose Issa Projects, London; Freies Museum, Berlin; as well as group exhibitions at The Marrakesh Art Biennale; Edge of Arabia, London; Photoqua, Paris; and Re-orientations at Rose Issa Projects; among others. His work is in the collections of the Los Angeles Museum of Contemporary Art, Los Angeles; the Victoria & Albert Museum, London; the Farjam Collection, Dubai; Institut des Cultures d’Islam, Paris; Kamel Lazaar Foundation, Tunisia; Virginia Museum of Fine Art, Richmond, VA; and more.