John Leslie was commissioned a 2nd Lieutenant in the Grenadier Guards. He was a veteran of the Anglo-Egyptian War of 1882. In 1883, he married Leonie Blanche Jerome of New York. In 1902, he saw active service during the Boer War and became a Lieutenant Colonel and the commanding officer of the 12th (Reserve) Battalion, Royal Inniskilling Fusiliers. He served as High Sheriff of County Monaghan in 1905. He was appointed Honorary Colonel of the 5th Battalion, Royal Irish Fusiliers. In 1916, he succeeded to the baronetcy (Leslie of Glaslough) that had been granted to his father. Sir John was invested a Commander of the Order of the British Empire (CBE) in 1919. He served as the last Lord Lieutenant of County Monaghan, from 1921 to 1922, prior to the establishment of the Irish Free State.
Leonie Blanche Jerome Leslie
1859–1943 (m. 1884)