Leslie Fox was born in Yorkshire in 1918, and spent most of his professional life in Oxford, as Director of the University Computing Laboratory and as the first Professor of Numerical Analysis in the University.

His mathematical education began at the Wheelwright Grammar School in Dewsbury, which produced a number of distinguished mathematicians and scientists at about the same time as Fox under the influence of an inspiring Headmaster and teacher (Leslie Sadler). Fox went to Oxford in 1936 as a scholar of Christ Church, and he gained a First Class Honours degree in Mathematics. He continued his studies for a DPhil under the direction of Professor Sir Richard Southwell, with a project in the area of computational and engineering mathematics which initiated some of the main interests of his career. His first appointment was at the Admiralty Computing Service in 1943; here he learnt the skills of table-making which he later used in a number of publications.

In 1945 Fox and several colleagues moved to the new Mathematics Division of the National Physical Laboratory. It was recognised at that time that the emerging technology of automatic computation would lead to requirements for effective mathematical methods which exploited the new machinery. The Mathematics Division embarked on an extensive programme of research in computational methods, in parallel with the construction of the Pilot ACE machine, which carried out its first computations in 1950. The Division remained a major source of ideas and methods in numerical mathematics for many years, with Fox taking a leading role until he was appointed to set up the Computing Laboratory in Oxford in 1957.