Leslie was born on 13 August 1913 at 17 Grovedale Road, Wavertree in Liverpool to Solomon, who was born in Belarus and worked as a tailor and a leather merchant, and Ray nee Leman and he had two younger brothers Arnold and Herbert. Leslie enlisted into the Rifle Brigade and records state that he died as a result of an accident.

Leslie is buried with a Cross on his headstone and evidence was sent to the CWGC to have his headstone changed to a Star of David. The CWGC advised that Leslie actually attested as Agnostic on his records when he enlisted. They will change his headstone to remove the Cross and leave no religious symbol.