During the following years he was much employed on important embassies in the king's interests, first to the pope to appeal against the excommunication pronounced in July 1533, afterwards to the Emperor to dissuade him from attending the general council which the pope wished to summon at Vicenza. Towards the end of 1535 he was sent to further what he called "the cause of the Gospel" ("Letters and Papers", 1536, No. 469) in North Germany; and in 1536 he wrote a preface to Stephen Gardiner's "De vera Obedientia", which asserted the royal and denied the papal supremacy, and was received with delight by the Lutherans. After a brief embassy to the Emperor in the spring of 1538, Bonner succeeded Gardiner as ambassador to the French Court in Paris. In this capacity he proved capable and successful, though irritation was frequently caused by his overbearing and dictatorial manner. He began his mission by sending Cromwell a long list of accusations against his predecessor. He was almost as bitter against Wyatt and Mason, whom he denounced as a "papist", and the violence of his conduct led Francis I to threaten him with a hundred strokes of the halberd. He seems, however, to have pleased his patron, Cromwell, and perhaps Henry, by his energy in seeing the king's "Great" Bible in English through the press in Paris. He was already king's chaplain; his appointment at Paris had been accompanied by promotion to the See of Hereford (27 November 1538) but owing to his absence he could neither be consecrated nor take possession of his see, and he was still abroad when he was translated to the Bishopric of London (October 1539). Bonner returned to England and was consecrated 4 April 1540.