He was the son of William de Warenne, the only son of John de Warenne, 6th Earl of Surrey. His mother was Joan, daughter of Robert de Vere, 5th Earl of Oxford. Warenne was only six months old when his father died, and was 8 years old when his mother died. He succeeded his grandfather as earl when he was 19.
He was one of the great nobles offended by the rise of Edward II's favorite Piers Gaveston, and helped secure Gaveston's 1308 banishment. The two were somewhat reconciled after Gaveston's return the next year, but in 1311 Warenne was one of the nobles who captured Gaveston. He was however unhappy about Gaveston's execution at the behest of the earl of Warwick, which pushed him back into the king's camp.
The baronial opposition was led by the king's cousin Thomas, Earl of Lancaster, and he and Warenne became bitter enemies. Private war erupted between the two, and over the next few years Warenne lost a good part of his estates to Lancaster.
Warenne and his brother-in-law Edmund Fitzalan, 9th Earl of Arundel, were the last two earls to remain loyal to Edward II after the rise to power of Queen Isabella and Roger Mortimer. After Arundel's execution he went over to the queen's side, urging Edward II's abdication in 1327.
He was the guardian of his cousin Edward Balliol, and after Balliol lay claim to the Scottish throne, accompanied him on his campaign in Lothian. Balliol created Warenne earl of Strathern, but this was in name only for the properties of the earldom were held by the Scots.