His mother was Matilda (born 1298), also called Agnes, elder daughter and coheiress of Brian FitzAlan, lord of Bedale, Askham Bryan, and Cotherstone.
Through his paternal line, he was a great-grandson of Dervorguilla of Galloway, mother of John Balliol, King of Scotland, and a descendant of the Bruces by Laderia, daughter of Peter III de Brus of Skelton and grandmother of Sir Gilbert.
[2][3] Only an infant at the death of his father, he was at the Siege of Tournai (1340) with his younger brother Brian Stapleton, and then fought in Brittany during the War of Breton Succession.
He participated in three tournaments between October 1347 and January 1348, at Bury St Edmunds, Eltham, and Windsor, after which he was described as a knight of the chamber in the Wardrobe accounts.
In January 1363, Stapleton was one of a group of English knights recorded as borrowing money from local merchants at Toruń in Poland, most likely during a Prussian crusade.