Leslie was born on 15 March 1922 in Willesden, Middlesex to Sidney and Blanche née Bresler and had three younger siblings, Milton, Michael and Lorraine. The family lived in Canada for a time where their father Sidney worked as a civil servant. The family returned to England in 1932 and moved to Leicester where Sidney was a tailors shop manager.

Leslie was killed on his sixth operation. He was the navigator of Lancaster ND840 which departed from RAF Coningsby on a daylight bombing operation to Bois de Cassan V1/V2 flying bomb site. The aircraft was hit by flak which incapacitated F/O Bucknell and it crashed at Eaubonne (Val d’Oise) a small town roughly 14 km ESE of Pontoise. Details of his operations can be found on the link below.