Thomas Buddle was born at Durham, England, probably on 24 December 1812, the son of Matthew Buddle, a cordwainer, from a prominent Anglican family, and his wife, Mary Anderson. At the age of 17 Thomas joined the Wesleyan Methodist Church, becoming a lay preacher. In 1835 he was accepted as a probationer, and was ordained by the Wesleyan Methodist Conference at Liverpool in 1839. On 16 August 1839 he married Sarah Dixon at Barnard Castle, Durham; they were to have 10 children. Buddle accepted a call to serve in New Zealand from the general committee of the Wesleyan-Methodist Missionary Society, and he and Sarah departed Bristol in the society's ship, Triton, in September 1839, arriving at Hokianga in May 1840.
Buddle was first stationed at Whāingaroa (Raglan Harbour), but a few months later was dispatched to Porirua; his vessel was wrecked at Kāwhia, and Buddle returned to Whāingaroa. In December 1840 he was appointed to Waipā (West). Initially he established himself at Honipaka, but when Pōtatau Te Wherowhero objected that the site was a sacred place, he shifted instead to Te Kōpua in May 1841. Between 1841 and 1844 he baptised many leading Māori, and opened schools between the upper Mōkau River and Lake Taupō. In May 1844, in company with John Morgan, John Whiteley and James Wallis, Buddle accompanied local Māori to the great Waikato feast at Remuera.
Buddle's organisational ability led, in 1844, to his appointment as head of the Wesleyan Native Institution in Auckland, a college devoted to training Māori teachers. For the next 21 years he ministered to Māori and Pākehā congregations in Auckland. He also served as one of the Wesleyan representatives on the Māori Bible Revision Committee.
Increasingly drawn into church administration, Buddle attended the church's seventh Australasian conference in Sydney in 1861, and was appointed its secretary. He was president of the ninth conference, held at Hobart in 1863. He served on a series of circuits – Manukau (1854–60), Auckland (1861–65), Christchurch (1866–69), Wellington (1870–72) and Nelson (1873–75) – and was successively chairman of the Auckland, Wellington and Christchurch districts. When the Wesleyan Methodist Church in New Zealand gained its independent conference in 1874, Buddle served as its first president. From 1875 to 1881 he served as founding principal of Three Kings Theological and Training Institution (later Wesley College).
In the early 1860s Buddle's knowledge of the Māori increasingly drew him into political affairs. He edited Māori-language newspaper Te Haeata, which was published from 1859 to 1862. The newspaper was religious, but also contained some political content. In May 1860 Thomas Buddle, Donald McLean, John Williamson, Bishop G. A. Selwyn and other missionaries attended a large King movement meeting at Ngāruawāhia. Buddle's attitude to the movement was expressed in his pamphlet of that year, The Māori King movement in New Zealand. He regarded it as an attempt to repudiate the sovereignty of the Crown, and claimed that Māori possession of large tracts of uncultivated land retarded their progress towards civilisation, fostered covetousness and indolence, and led to intertribal squabbling and wars; he added, somewhat incongruously, that the Treaty of Waitangi should nevertheless be kept in good faith.
In spite of his opposition to the King movement, Buddle did not advocate war, partly because he thought the movement's lack of unity contained within it the seeds of its own destruction. Nevertheless the Wesleyan church, fearing that war would be a setback to the progress they had made in Waikato, sent Thomas Buddle, James Wallis and Alexander Reid on a mission to detach the Waikato tribes from the King movement. The mission failed, as they found Ngāti Maniapoto determined to go to war if provoked. Buddle had also underestimated the determination of the colonists to see Waikato opened up for settlement. He restrained the more aggressive supporters of a military solution among the missionaries, such as John Hobbs, Samuel Ironside and John Warren, although he himself conveyed intelligence to Governor George Grey. By 1864 the Māori saw the Wesleyans as having supported the war, and the growth of the church in Waikato accordingly received a check.
Buddle's knowledge of Māori language, customs and culture resulted in his delivering in 1851 two lectures on 'The aborigines of New Zealand'; and in 1873 two lectures on 'Christianity and colonisation among the Māori', in which he invoked biblical texts and divine providence in support of European colonisation of New Zealand. Grey drew on his knowledge when compiling his Polynesian mythology.
Buddle was a member of the senate of the University of New Zealand from 1874 to 1880, and a member of the council of Auckland University College. He died in Auckland on 26 June 1883, having helped lay the foundations for an expanding and vigorous colonial Methodism.