[3] After graduating from Cambridge, Selwyn worked at Eton College, becoming assistant master and tutoring the sons of Edward Herbert, 2nd Earl of Powis.

In 1833 he was ordained deacon, and in 1834, a priest; he acted as curate to Isaac Gosset, the vicar of St John's, Windsor from 1833 until 1841.

The boat hit a rock on landing and, rather than wait for its repair, some of the party, including Selwyn and Cotton, set sail for New Zealand on the brig Bristolian on 19 May.

[6][7] After spending some time as guests of Captain William Hobson, the first Governor of New Zealand, Selwyn and Cotton set sail on 6 June on the schooner Wave to visit the mission stations on the Hauraki Gulf, then north to the Bay of Islands.

[10] In June 1842, Selwyn set up residence at Te Waimate mission,[11] some 15 miles (24 km) inland from Paihia where the Church Missionary Society (CMS) had established a settlement 11 years earlier.

[11] On 5 July 1842 Selwyn set out on a six-month tour of his diocese leaving the Mission Station in the care of Sarah, his wife, and Cotton.

[8] By October 1843, more missionaries had arrived at Waimate, and Selwyn, accompanied by Cotton, embarked on his second tour, this time to mission stations and native settlements in the southern part of North Island.

[15] The staff and students lived in huts at the head of the Purewa Creek which served as the port while the college was constructed upstream.

There was often a wide gap between the views of the CMS missionaries and the bishops and other clergy of the high church traditions of the Oxford Movement (also known as the Tractarians) as to the proper form of ritual and religious practice.

In six years he completed a thorough visitation of the whole of New Zealand, and in December 1847 began a series of voyages to the Pacific Islands, which were included in his diocese by a clerical error in his letters patent.

[25] His letters and journals descriptive of these journeyings through Melanesia present the reader with a vivid picture of his versatility, courage, and energy.

In 1854 he visited England to secure authorisation to subdivide his diocese, as well as permission for the church of New Zealand to manage its own affairs by a "general synod" of bishops, presbyters, and laity.

The CMS had funded half of his role on the condition that he ordain as many people as possible, but Selwyn slowed this down by insisting those in training learn Greek and Latin first.

[31] Selwyn generally advocated for Māori rights and was often a critic of the unjust and reckless land acquisition practices that led to the New Zealand Wars.

In the letter he further held that military action should not have been engaged in before exploring 'civil power' to resolve the dispute, called for a full scale investigation and concluded that Māori deserved the government's 'respect and gratitude...[instead of]...bullets'.

[32] However his support of the Invasion of the Waikato, where, as chaplain, he was frequently seen riding on horseback on the frontlines with the British and colonial forces, and his involvement in the burning of women and children at Rangiaowhia in 1864,[33] damaged his and the church's relationship with Māori, which is still felt today.

[36]: p.34 In 1867, Selwyn visited England a second time to participate at the first Pan-Anglican synod of the Lambeth Conference, an institution which his own work had done much to bring about.

Earlier that year, Bishop Selwyn had ordained a class of deacons, one of whom, John Roberts, is known for his missionary work in the Bahamas and Wyoming.

The college's first Master, Arthur Lyttelton, was elected on 10 March 1879, the Archbishop of Canterbury Archibald Tait was invited to become Visitor on 28 June 1878, and the college's founders purchased a six-acre (24,000 m2) farm land site between Grange Road, West Road and Sidgwick Avenue on 3 November 1879 at a cost of £6,111 9s 7d and the building of Old Court, as it is now known, began in 1880.

A Charter of Incorporation was granted by Queen Victoria on 13 September 1882, and the west range of Old Court was ready for use by the college's official opening (with the Master's installation) on 10 October 1882.

The foundation charter specified that the college should "make provision for those who intend to serve as missionaries overseas and... educate the sons of clergymen".