 In September he was made Steward of the King's Household, Keeper of Kent, Surrey and Sussex, and in December was appointed Lord Warden of the Cinque Ports and made High Sheriff of Kent.In October 1263 he was one of those who sealed the agreement between Henry and Louis IX, and travelled with the king to France at the end of the year.During the second half of the conflict with de Montfort, Leybourne fought at the Battle of Northampton and as a defender at the siege of Rochester Castle, where he was badly wounded.