Lord of the manors of Tanfield and Well, Yorkshire. De Mowbray served in the Scottish wars of Edward I. The baron held such offices as sheriff of Yorkshire, governor of the city of York, a warden of the Scottish marches, governor of Malton and Scarborough Castles. He took part in the rebellion of Thomas, Earl of Lancaster.
He was captured at the battle of Boroughbridge and subsequently hanged at York. John de Mowbray married Aline de Braose, (b 1291 d ca 1331), daughter of William de Braose, 2nd Baron Braose and Lord of Gower. They had at least two sons:
29 November 1310, Yorkshire, England d.1361 who succeeded his father to the barony. Alexander, (c 1314 – c 1391).