It was very largely Winchelsey's achievements as a man of learning that led to his appointment to high office in the Church. At Oxford he had been one of a group of eminent secular masters which included three future bishops: John of Monmouth (bishop of Llandaff 1297–1323), Simon of Ghent (bishop of Salisbury 1297–1315) and John Dalderby (bishop of Lincoln 1300–20); and another scholar, probably known to the group, was a secular master at Cambridge: Ralph Walpole (bishop of Norwich 1289–99, and bishop of Ely 1299–1302). There is no evidence of a close relationship at any stage in their careers between Dalderby and Winchelsey, though more would be known of Dalderby's episcopate if his registers were in print. Walpole gave moderate support to the archbishop during the critical year of 1297. But both Monmouth and Ghent were strong supporters of Winchelsey during that year, and with both these bishops Winchelsey formed lasting friendships. Simon had acted as responding bachelor at Winchelsey's inception as a regent-master; and Winchelsey had presided at the vesperies of John of Monmouth. Both Simon and John succeeded Winchelsey as chancellors of the university of Oxford. The appointment of John to the see of Llandaff, which had been vacant since 1287, was, unusually, the sole responsibility of the archbishop. Immediately after his consecration in 1294 Winchelsey sought to remedy the difficult situation concerning the see of Llandaff, and Celestine V granted him the authority to collate the bishopric.