Sir John Leslie, 1st Baronet (16 December 1822 – 23 January 1916) was the son of Charles Powell Leslie (II) and grandson of Charles Powell Leslie (I) and his uncle was the Bishop, John Leslie. Leslie was a Conservative Member of Parliament for Monaghan from 1871 to 1880. He succeeded his elder brother, Charles Powell Leslie III, in that role.
In 1830, he was sent to school at Dedham, Essex. During midsummer term, 1834, he joined his elder brother, Charles, at Harrow. In 1839, John entered Christ Church, Oxford. He obtained a commission in the 1st Life Guards, and was quartered at the Regent's Park, Hyde Park, Windsor, and Farnborough barracks.
In 1854, he met at Hazelwood a distinguished Waterloo veteran, Colonel George Dawson-Damer (younger brother of the 2nd Earl of Portarlington), and his daughter, Constance. Leslie married Miss Damer two years later at St George's, Hanover Square, London. His new mother-in-law, Mrs Damer ("Minnie Seymour"), was the adopted daughter of George IV's wife, Maria, Mrs Fitzherbert.
Sir John and Lady Constance Leslie had one son and four daughters:
