he served on commissions to visit the university of Oxford, to inquire into heresies, to examine the charges against Lord Seymour of Sudeley, and to try Bonner. He did not take part in Bonner's trial after the first day, and it was rumoured that he ‘was turning about to another party.’ On 6 Oct. he was sent by Somerset to the council to demand the reason of their coming together, but, finding them the stronger party, he remained and signed the council's letter to the lord mayor denouncing the protector; four days later he also signed the proclamation against Somerset. In February 1550 he was sent to Boulogne to negotiate the terms of peace with France, and in the following May exchanged ratifications of it at Amiens. In the same year he was treasurer of firstfruits and tenths, and one of the commissioners to examine Gardiner; he was also sent to New Hall, Essex, to request Mary to come to court or change her residence to Oking. In August 1551 Petre was one of those who communicated to Mary the council's decision forbidding mass in her household, and in October was appointed to confer with the German ambassadors on the proposed protestant alliance; in December he was on a commission for calling in the king's debts. In 1553 he drew up the minutes for Edward VI's will and, in the interest of Lady Jane Grey, signed the engagement of the council to maintain the succession as limited by it. On 20 July, however, he, like the majority of the council, declared for Mary. He remained in London during the next few days transacting secretarial business, but his wife joined Mary and entered London with her.
Petre had been identified with the council's most obnoxious proceedings towards Mary, and his position was at first insecure. He resumed attendance at the council on 12 Aug., but in September it was rumoured that he was out of office. He was, however, installed chancellor of the order of the Garter on 26 Sept., when he was directed by the queen to expunge the new rules formulated during the late reign. He further ingratiated himself with Mary by his zeal in tracing the accomplices of Wyatt's rebellion and by his advocacy of the Spanish marriage. Petre now devoted himself exclusively to his official duties; he rarely missed attendance at the council, and was frequently employed to consult with foreign ambassadors. He acquiesced in the restoration of the old religion, and took a prominent part in the reception of Pole and ceremonies connected with the absolution of England from the guilt of heresy. But with great dexterity he succeeded in obtaining from Paul IV a bull confirming him in possession of the lands he had derived from the suppression of the monasteries (Dugdale, Monasticon, vi. 1645). It was on his advice that Mary in 1557 forbade the landing of the pope's messenger sent to confer legatine power on William Peto [q. v.] instead of Pole. Owing to declining health he ceased to be secretary in 1557.
On Elizabeth's accession Petre was one of those charged to transact all business previous to the queen's coronation, and was still employed on various state affairs, but his attendances at the council became less frequent. They cease altogether after 1566, and Petre retired to his manor at Ingatestone, Essex, where he devoted himself to his charitable foundations. He died there, after a long illness, on 13 Jan. 1571–2, and was buried in Ingatestone church, where a handsome altar-tomb to his memory, between the chancel and south chapel, is still extant.
Petre's career is strikingly similar to those of other statesmen of his time, such as Cecil, Mason, and Rich, who, ‘sprung from the willow rather than the oak,’ served with equal fidelity Henry, Edward, Mary, and Elizabeth. Camden calls him ‘a man of approved wisdom and exquisite learning,’ and Strype says he was ‘without spot that I could find except change of religion.’ He was ‘no seeker of extremity or blood, but of moderation in all things.’ As a diplomatist his manner was ‘smooth, reserved, resolved, yet obliging:’ ‘Ah!’ said Chatillon of Petre at Boulogne in 1550, ‘we had gained the last two hundred thousand crowns without hostages, had it not been for that man who said nothing.’ In his later years he was said to be a papist, a creed to which his descendants have consistently adhered. But his piety was not uncompromising, and did not stand in the way of his temporal advancement; as he himself wrote to Cecil, ‘we which talk much of Christ and his holy word have, I fear me, used a much contrary way; for we leave fishing for men, and fish again in the tempestuous seas of this world for gain and wicked mammon.’ Though he was less rapacious than his colleagues in profiting by the fall of Somerset, Petre acquired enormous property by the dissolution of the monasteries; in Devonshire alone he is said to have secured thirty-six thousand acres; but his principal seat was at Ingatestone, Essex, which he received on the dissolution of the abbey of St. Mary's, Barking. The hall which he built there still stands almost unimpaired (cf. Barrett, Essex Highways, &c., 2nd ser. pp. 32, 178–80). A considerable portion of his wealth, however,
