St. Leger faithfully served Edward IV in both a military and administrative capacity for years. For his loyal service, Edward IV rewarded St. Leger with a substantial grant of eight manors in the early 1460s. He had a lucky escape from justice in 1465 when he was arrested for brawling in the Palace of Westminster and sentenced to have his hand cut off. Edward IV, however, granted him a pardon. Thomas fought for Edward at the Battles of Barnet and Tewkesbury. St Leger played a key role in ending the Hundred Years' War when he signed the Treaty of Picquigny with Louis XI on 29 August 1475. He was granted by Louis XI a pension of 12,000 crowns annually which was to be distributed between himself, Thomas Grey, 1st Marquess of Dorset, Sir John Howard (later Duke of Norfolk), Sir Thomas Montgomery, and some other of the profligate courtiers. Thomas was also knighted as a member of the Order of the Bath.