Leigh was one of the few West Africans to enlist and serve in the Second World War as a bomber pilot in the British Royal Air Force.
Thomas William "Dupi" Leigh was a paternal descendant of William Henry Leigh, an English slave trader and a maternal descendant of the Dupigny family of Freetown, Sierra Leone, originally of African and French-Dominican descent in Roseau, Dominica.
Leigh attended St Anthony's Primary School and subsequent to completing his secondary school education at the Albert Academy, Leigh travelled to Britain and enlisted in the Royal Air Force.
William Leigh was appointed the first African Commissioner of Police following the independence of Sierra Leone on 27 April 1961.
William Leigh died of a heart attack in Monrovia, Liberia.