As a politician, the period of Courtenay's activity coincides with the years of Edward III's dotage, and with practically the whole of Richard II's reign. From the first he ranged himself among the opponents of John of Gaunt, duke of Lancaster; he was a firm upholder of the rights of the English Church, and was always eager to root out Lollardry. In 1373 he declared in convocation that he would not contribute to a subsidy until the evils from which the church suffered were removed; in 1375 he incurred the displeasure of the king by publishing a papal bull against the Florentines; and in 1377 his decided action during the quarrel between John of Gaunt and William of Wykeham ended in a temporary triumph for the bishop.