Thomas Barker Leigh was born on 11 February 1919 in Waverley, New South Wales, to Constance Emily Carena (née Barker) and David Leigh. The Leigh family spent Thomas' youth living in England and Shanghai, where his mother died in 1926 and his father in 1932. Thomas and his two siblings remained in the United Kingdom following their father's death and, on leaving school, Thomas spent a period aboard the naval training ship Mercury in Hampshire.
Leigh subsequently applied for the Royal Air Force (RAF) and was accepted as part of the 32nd Entry of RAF Apprentices to No. 1 School of Technical Training at RAF Halton on 20 August 1935. He trained as an engine aero fitter, was promoted to leading apprentice in August 1936 and, on qualifying as a Fitter II in June 1938, was posted to No. 48 Squadron as an aircraftman 2nd class. In July 1939, Leigh was accepted for aircrew training and, following the outbreak of the Second World War, was promoted leading aircraftman on 31 December.
Leigh qualified as an air gunner in March 1940 and, on 31 December, was promoted to sergeant. He was transferred to No. 76 Squadron five months later, on 27 May 1941, and was commissioned a pilot officer (on probation) on 2 August. The following evening, Leigh took part in a bombing raid on Berlin.
On the night of 5/6 August 1941, Leigh's Halifax bomber failed to return from a raid on Karlsruhe, Germany. The aircraft is believed to have crashed near Glabbeek, Belgium, and Leigh was later confirmed to be a prisoner of war. While in captivity, Leigh was promoted to flying officer on 2 August 1942 and to flight lieutenant on 2 August 1943.
Leigh was later sent to Stalag Luft III in Sagan, Lower Silesia. In March 1944, he was one of 76 Allied prisoners to attempt a mass escape from the camp (colloquially known as the 'Great Escape'); all but three were recaptured. Leigh was handed over to the Gestapo and taken to Görlitz prison. There, on 31 March 1944, he was murdered by Gestapo agents in reprisal for the escape.
Leigh was posthumously Mentioned in Despatches in June 1944. He is buried in Poznan Old Garrison Cemetery, Poland.