Leslie was born on 28 February 1914 in Grimsby, Lincolnshire to Solomon and Henrietta née Friend and he had two older siblings, Cyril and Gertrude. Their father Solomon worked as a pawnbroker and died in 1935. Leslie attended Sir Moses Montefiore Synagogue and was a pupil at Clee Grammar School. He is commemorated on memorials at both the synagogue and school.

Leslie enlisted into the RAF as a pilot in 1937 and in 1939 he was living at 175 Gloucester Place, St Marylebone.

Leslie was the pilot of Blenheim L8871 which departed RAF Weston on the Green on a day training exercise. One engine cut out causing the aircraft to swing out of control and crash. All three crew were killed when the aircraft caught fire.

W/Op, William Alfred Dismore, 652610

U/T Observer, James Francis Ferguson Kerr, 748075