College, Cambridge, during 1809–10, and in the latter year Sumner was superannuated, having previously been elected Davis's scholar. He was consequently entered at Trinity College, Cambridge, on 17 Feb. 1810, and then went to Sedbergh for a few months to read mathematics with a popular tutor called John Dawson, after which he made a short tour in the Lakes, calling on Coleridge and Wordsworth. He matriculated on 13 Nov. 1810, and was admitted scholar on 10 April 1812. He graduated B.A. in 1814 and M.A. in 1817. On 5 June 1814 he was ordained deacon, and on 2 March 1817 priest. At Cambridge he was the last secretary of the ‘Speculative’ Society, afterwards merged in the body known as the ‘Union.’
In the summer of 1814 Sumner accompanied Lord Mount-Charles (who had been a fellow undergraduate at Trinity College), and Lord Francis Nathaniel Conyngham, the eldest and second sons of Marquis Conyngham, through Flanders and by the Rhine to Geneva, where he unexpectedly met J. T. Coleridge; Coleridge introduced them to J. P. Maunoir, M.D., professor of surgery in the college of that city. The professor's wife was an English lady, and to the eldest of their three daughters, Jennie Fanny Barnabine, Sumner became engaged in January 1815. Gossip asserted that he took this step to forestall similar action on the part of the elder of his pupils, whose father secured Sumner's preferment in the church by way of showing his gratitude. During the winter months of 1814–15 and the autumn and winter of 1815–16 he ministered to the English congregation at Geneva. On 24 Jan. 1816 he married Miss Maunoir at the English chapel of Geneva. From September 1816 to 1821 Sumner served as curate of Highclere, Hampshire, and took pupils, Lord Albert Conyngham and Frederick Oakeley being among them.
In 1820 Sumner was introduced by the Conynghams to George IV at Brighton, where he dined with the king, and talked with him afterwards for three hours. His handsome presence, dignified manners, and tact made a most favourable impression. In April of the following year George, without waiting for the approval of Lord Liverpool, the prime minister, announced to Sumner that he intended to promote him to a vacant canonry at Windsor. The prime minister refused to sanction the appointment, and an angry correspondence took place between king and minister (Yonge, Life of Lord Liverpool, iii. 151–4). For a time it seemed as if the offer of this desirable preferment to the young curate might jeopardise the life of the ministry, but George IV reluctantly gave way. A compromise was effected. The canonry was given to Dr. James Stanier Clarke [q. v.], and Sumner succeeded to all Clarke's appointments. These included the posts of historiographer to the crown, chaplain to the household at Carlton House, and librarian to the king, and George IV also made him his private chaplain at Windsor, with a salary of 300l. a year, ‘and a capital house opposite the park gates.’ Other promotions followed in quick succession. From September 1821 to March 1822 (in 1822 his first and last sermons in the church were published in one volume) he was vicar of St. Helen's, Abingdon; he held the second canonry in Worcester Cathedral from 11 March 1822 to 27 June 1825, and from the last date to 16 June 1827 he was the second canon at Canterbury. He became chaplain in ordinary to the king on 8 Jan. 1823, and deputy clerk of the closet on 25 March 1824. In January 1824 the new see of Jamaica was offered to him, but George IV refused to sanction his leaving England, asserting that he wished Sumner to be with him in the hour of death, and in July 1825 he took at Cambridge, by the king's command, the degree of D.D. On 27 Dec. 1824 he was with Lord Mount-Charles when he died at Nice.
On 21 May 1826 Sumner was consecrated at Lambeth as bishop of Llandaff, and in consequence of the poverty of the see he held with it the deanery of St. Paul's (25 April 1826), and the prebendal stall of Portpoole (27 April 1826). Within a year he made his first visitation of the diocese. When the rich bishopric of Winchester became vacant in 1827 by the death of Dr. Tomline, the king hastened to bestow it upon Sumner, remarking that this time he had determined that the see should be filled by a gentleman. Sumner was confirmed in the possession of the bishopric on 12 Dec. 1827, and next day was sworn in as prelate of the order of the Garter. He was just 37 years old when he became the head of that enormous diocese, with its vast revenues and its magnificent castle.
Though he opposed the Reform Bill in 1832, the strong tory views which he held in early life were soon modified. He voted for the Roman Catholic Relief Bill of 1829 (a step which he regretted later), with the result that he forfeited the affection of George IV, and another prelate was summoned to attend the king's deathbed (Southey, in Letters of Lake Poets to Stuart, p. 427).
One of the first acts of Sumner as bishop of Winchester was to purchase with the funds of the see a town house in St. James's Square,
