Aymer was the son of
William de Valence, son of
Hugh X of Lusignan, and
Isabella of Angoulême. William was
Henry III's half-brother through his mother's prior marriage to King
John, and as such gained a central position in the Kingdom of England. He had come to the
earldom of Pembroke through his marriage to
Joan de Munchensi, granddaughter of
William Marshal. Aymer was the third son of his family, so little is known of his birth and early years. He is believed to have been born some time between 1270 and 1275. As his father was on
crusade with Lord
Edward until January 1273, a date towards the end of this period is more likely. The later date is problematic, however, because his mother by then was in her mid-forties. With the death in battle in Wales of his remaining brother William in 1282 (John, the elder brother, was dead in 1277), Aymer found himself heir to the earldom of Pembroke. William de Valence died in 1296, and Aymer inherited his father's French lands, but had to wait until his mother died in 1307 to succeed to the earldom. In 1320, his first wife Béatrice de Clermont died. In 1321, Aymer married his second wife
Marie de St Pol. Through inheritance and marriages his lands consisted of—apart from the
county palatine in Pembrokeshire—property spread out across England primarily in a strip from
Gloucestershire to
East Anglia, in south-east Ireland (
Wexford), and French lands in the
Poitou and
Calais areas. In 1297 he accompanied
Edward I of England on a campaign to
Flanders, and seems to have been knighted by this time. With his French connections he was in the following years a valuable diplomat in France for the English king. In 1302 he was amongst the team of
plenipotentiaries appointed by Edward I to negotiate the
Treaty of Paris that returned Gascony to Edward. He also served as a military commander in Scotland, fighting against
Robert the Bruce. In 1306 at the
Battle of Methven he won the day over Bruce in a sneak attack, only to be soundly defeated by Bruce at
Loudoun Hill the next year. ==Ordinances and Piers Gaveston==