Thomas and his younger brother Henry served in the coronation of their cousin King Edward II of England on 25 February 1308; Thomas carried Curtana, the Sword of Mercy, and Henry carried the royal sceptre. After initially supporting Edward, Thomas became one of the Lords Ordainers, who demanded the banishment of Piers Gaveston and the governance of the realm by a baronial council. After Gaveston was captured, Thomas took the lead in his trial and execution at Warwick in 1312. Edward's authority was weakened by poor governance and defeat by the Scots at the Battle of Bannockburn. This allowed Thomas to restrain Edward's power by republishing the Ordinances of 1311. Following this achievement Thomas took little part in the governance of the realm and instead retreated to Pontefract Castle. This allowed Edward to regroup and re-arm, leading to a fragile peace in August 1318 with the Treaty of Leake. In 1321 Edward's rule again collapsed into civil war. Thomas raised a northern army but was defeated and captured at the Battle of Boroughbridge. He was sentenced to be hanged, drawn and quartered but because he was Edward's cousin he was given a quicker death by beheading.