Thomas de Berkeley was born in 1245 at Berkeley Castle in the English county of Gloucestershire, the son of Sir Maurice de Berkeley and Isabel FitzRoy. Isabel FitzRoy was the granddaughter of John, King of England, by his cousin and mistress, Adela de Warenne, daughter of Hamelin de Warenne and Isabel de Warenne, 4th Countess of Surrey.
In 1267, Thomas de Berkeley married Joan de Ferrers, the daughter of William de Ferrers, 5th Earl of Derby and Margaret de Quinci. Thomas de Berkeley is also known by his epithet Thomas "the Wise". He fought in the Battle of Evesham.
He inherited the title of Baron de Berkeley in 1281 and was created 1st Baron Berkeley on 28 June 1283.
He was a commissioner to examine the claims to the crown of Scotland in June 1292. He was on an embassy to France in January 1296 and held the office of Vice-Constable of England in 1297.
He fought in the Battle of Falkirk on 22 July 1298 and fought in the siege of Caerlaverock in July 1300. He was on an embassy to Pope Clement V in July 1307.
He fought in the Battle of Bannockburn on 24 June 1314, where he was taken prisoner, and paid a large sum for his ransom.
He died at Berkeley on 23 July 1321. The children of Thomas de Berkeley, 1st Baron Berkeley and Joan de Ferrers are:
Alice de Stourton
Thomas de Berkeley. Ancestor of the Berkeleys of Wymondham
John de Berkeley (d circa 1317)
James de Berkeley
Isabel de Berkeley
Margaret de Berkeley (d circa 1320), has issue.
Maurice de Berkeley, 2nd Baron Berkeley (April 1271 - 31 May 1326), has issue.
