[6] He was given seisin of the lands of his inheritance from his grandfather, the late John de Warenne, 6th Earl of Surrey, in April 1306.

[7] 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.

[7] In 1319, the King granted the Earl of Lancaster the towns of Conisboro and Sandal, along with the manors of Wakefield, Thorne, Hatfield, Sowerby, Braithwell, Fishlake, Dewsbury, and Halifax with their appurtenances, which were held of the King in capite, and which John de Warenne had previously held under Royal Grant.

Balliol created Warenne earl of Strathern, but this was in name only for the properties of the earldom were held by the Scots.

John gave instruction in his will that he wished to be buried in an arch at the church which he had prepared near the high altar.

[7] On 15 March 1305, King Edward I of England offered John the marriage of his granddaughter Joan of Bar, Countess of Surrey, which he "willingly accepted.

A dispensation was granted from Pope Clement V in order for the marriage to take place, due to them being related within the fourth degree of kindred.

[21] There were soon indicators that this marriage may not be a happy one, when in 1309 king Edward II of England granted leave for John to make any person he wished heir to the lands that he held.

"[28][b] This description occurred during a notice delivered by "Robert, called of the chapel of Jackesle, a clerk of the diocese of Lincoln," to Joan of Bar that she was cited to appear before Thomas Gerdeston, the Archdeacon of Norfolk or his commissary to answer in a case of matrimony and divorce between herself and John de Warenne.

He granted Maud, and the Earl of Surrey, along with any other person that they may bring forward in their causes, protection pending the suits.

In John's case this was probably due to the fact that it was forbidden under church law for a man to bring divorce proceedings based on consanguinity.

[35] There were other obvious issues with the Earl's case: A dispensation had been obtained from the Pope at the time of marriage because John and Joan were related.