St. Leger was baptised on 1 May 1733 in
County Kildare, Ireland. He was a younger son of
Sir John St Leger, a leading Irish judge and politician, and his second wife Lavina Pennefather. He was the brother of Gen.
Anthony St Leger (British Army officer), the founder of the
St Leger Stakes. The St Legers of Kildare were a junior branch of the family of
Viscount Doneraile, and the Pennefathers were a wealthy landowning family in
County Tipperary. He was educated at
Eton College, and then at
Peterhouse, Cambridge. He joined the
British Army in April 1756, serving as an ensign in the
28th Regiment of Foot. He saw service in the
French and Indian War under the command of
Jeffery Amherst at the 1758
siege of Louisbourg, and in 1759 under the command of
James Wolfe at the
Siege of Quebec. He was appointed
brigade-major in July 1760 and served as a staff officer in the campaign against
Montreal under
James Murray. On 16 September 1762, St. Leger was promoted to major in the
95th Regiment of Foot. When reports of a relief force under
Benedict Arnold reached him, St. Leger was abandoned by his Native supporters and was forced to withdraw to Quebec. He then tried to join with Burgoyne's army near Saratoga but had only reached
Fort Ticonderoga by the time Burgoyne surrendered his army in October 1777. For the next several years, St. Leger was a leader of the British frontier war against the Americans. He was promoted to colonel in 1780. In 1781, he led an attempt to kidnap General
Philip Schuyler. He was also involved in
the secret negotiations between
Frederick Haldimand, Quebec's governor, and the
Vermont Republic's leaders over the possibility of bringing Vermont into the British fold. These negotiations ended with the
surrender of Cornwallis at Yorktown. His will was proved on 14 February 1794 at the PCC London by Frances St. Leger, widow. ==See also==