In 1974 Morris, then at school in London, heard that Bob Marley was playing at the Speakeasy Club in Great Marlborough Street, London. He went to the club during the day, met Marley and asked to take his picture. Marley agreed, and after hearing that Morris wanted to be a photographer told him “You are a photographer”. The following day Morris left with the band in their Transit van. He went on to photograph the musician until Marley's death in 1981.
Dennis's photos of Marley caught the eye of the young Johnny Rotten. Rotten, a massive reggae fan, had long admired Dennis's work and requested that he take the first official shots of the Sex Pistols upon signing to Virgin Records. Still in his teens, Dennis was the same age as the Pistols and they soon learned to trust him completely, allowing him unrestricted access to their strange and chaotic existence. For a year, Dennis trailed the band, taking hundreds of undisputed classic shots. The only photographer to put the Sex Pistols fully at ease in front of the lens, Dennis's work with the band established, not only their public image, but also Dennis's position as one of the most exciting and striking music photographers in the country.