Slocombe was born in Putney,London, the son of Marie (née Karlinsky) and journalist George Slocombe (1894–1963). His mother was Russian.His father was the Paris correspondent for the Daily Herald, and so Slocombe spent part of his upbringing in France, returning to the United Kingdom in around 1933.He graduated with a degree in Mathematics from the Sorbonne.

Slocombe initially intended to become a photojournalist, and as a young photographer, he witnessed the early events leading up to the outbreak of World War II.

After returning to England, Slocombe became a cinematographer for the Ministry of Information, shooting footage of Atlantic convoys with the Fleet Air Arm. He also developed a relationship with Ealing Studios, where filmmaker Alberto Cavalcanti, who helped him obtain his position, worked.Some of his photography was used as second unit material for fiction films.

Slocombe moved into photographing for feature films at Ealing Studios during the later 1940s, after being hired on the strength of his documentary work.Slocombe later described his early work on Champagne Charlie (1944) as amateurish, in one case resulting in a sequence having to be reshot.However, in his career, Slocombe worked on 84 feature films over a period of 47 years.

Slocombe would later speak approvingly of Ealing's culture of script development.[14] However, he also noted that its restrictive studio system headed by Michael Balcon, in which outside work was not normally permitted, made it impractical for him to attempt to begin a career as a director, something which he had considered.

In the 1980s, he worked with Steven Spielberg on the first three Indiana Jones films,but began to suffer from eyesight problems in the 1980s,and was nearly blind at the end of his life.His successor Janusz Kamiński,said that he deliberately shot the film to emulate Slocombe's visuals.In his later years, he lived in West London with his daughter, his only child.