Leslie Thornton was born on May 26, 1925, in Skipton, United Kingdom. He studied at Leeds College of Fine Art (1945–48), where his training focused primarily on antiquity and life drawing. Antiquity and especially early Cycladic terracotta figures had a lasting impact on Thornton, who at this time made regular trips to the British Museum for inspiration. He continued his studies at the Royal College of Art, where he became interested in contemporary painting and sculpture, particularly in metal.

Thornton’s early experimentations with linear drawing using steel and iron date from 1951, the year he graduated from the Royal College of Art. The same year he also joined the Royal Society of British Sculptors as an associate and began his teaching career as a visiting lecturer at the Bromley, Hammersmith, and Central Schools of Art. Subsequently he held teaching posts at the University of Sunderland and was principal lecturer and Head of the Sculpture Department at the University of Stafford from 1970 to 1989.

Abstraction and figuration, usually at opposite ends of the artistic spectrum, were for Thornton complementary modes which he moved seamlessly between. In 1955 his work was included in the New Sculptors Exhibition at the ICA in London. This same year he participated in the Young British Sculptors exhibition organized by the British Council, which traveled to Germany and Sweden. In 1957 his first solo exhibition was held at Gimpel Fils Gallery in London and throughout the course of the 1960s his works were included in group exhibitions in Holland, Switzerland, France, the United Kingdom, and the United States. At this time, Thornton was also commissioned a sculpture for the Daily Mirror Building in London (1961) and two crucifixes one for St Louis Priory, Missouri (1965) and one for St Ignatius College, Enfield (1968). In 2004 Thornton was included in the 100 Years of Sculpture exhibition at the Moore Institute in Leeds. Thornton died on February 9, 2016.