Hart-Davis's career in publishing began in 1929, when he joined William Heinemann Ltd as an office boy. After building up some knowledge of the area, he bought a stake in another publishing company, Jonathan Cape Ltd, which he joined as a director in 1933.
In 1946, Hart-Davis struck out on his own, founding Rupert Hart-Davis Ltd, under which name he published many books by authors both obscure and well-known. In the late 1960s and early 1970s he published a number of notable New Wave science fiction novels, including Thomas Disch's Camp Concentration. Other science fiction writers with work published by his company include Ray Bradbury, Angela Carter, and E. C. Tubb.
He had three children, who have all gone on to become noteworthy in their own right: Bridget Min Hart-Davis (born 1935) is married to the present Lord Silsoe; Duff Hart-Davis (born 1936) is a biographer and journalist; and Adam Hart-Davis (born 1943) is a well-known television broadcaster and author.