[1][2] His father was first cousin of Welsh rebel Sir Gruffydd Llwyd, while on his mother's side he was related to poet Dafydd ap Gwilym.
[2] He inherited from his grandfather substantial lands around Llansadwrn, in Carmarthenshire, and held several lucrative offices in the southwest of Wales,[2] as well as in 1308 being steward of Cardigan.
[2] With their downfall, and after in August 1327 he marshalled active support from North and South Wales in a conspiracy to release the imprisoned king Edward II of England,[3] he was forced to briefly flee to Scotland.
[2] He would continue to supply and lead men for the English campaigns against Scotland through 1341, and was the predominant captain of Welsh troops, mostly archers,[5] fighting for Edward in France, culminating in the Battle of Crecy in 1346, the same year he was knighted.
[8] Rhys was celebrated by Welsh poet Einion Offeiriad,[9] and memorialized in poems by his cousin Dafydd ap Gwilym, and by Iolo Goch.