 He was the only son of Sir John Leslie, 1st Baronet, and Lady Constance Wilhelmina Frances Dawson-Damer.His father was the Conservative Member of Parliament for Monaghan from 1871 to 1880 and was created a baronet in 1876.After his father's death in January 1916, Leslie succeeded his father as the 2nd Baronet Leslie, of Glaslough.