David Collins joined the Picture department of Knight, Frank & Rutley in 1965, and in 1967 he became assistant to the head of the Picture department at Debenham Coe. He took over as head of the department in 1971 and remained with the firm when it became Christie's South Kensington in 1975, becoming a director of the company. He was responsible for many important picture sales including those devoted to the paintings by Tim Keating in 1983 and 1984. In 1986 he became a member of the executive committee of Christie's South Kensington. Since 1988 he has been an independent consultant.