Thomas Mason was born in York, Yorkshire, England, on 28 July 1818, the first of three children of John Mason, a tea dealer, and his wife, Catharine Smart of Warwick. Both parents and their families were members of the Society of Friends (Quakers). Thomas's father died in 1822 at the age of 33, and around 1833 his mother married again. She moved to America with the two younger children, leaving Thomas in the care of his uncles and aunts. He attended Bootham School from 1829 to 1832 and then worked in business and farming. On 16 November 1840 at Bishophill, York, he married Jane Morris of Upper Poppleton. He resigned from the Society of Friends to avoid being disowned – as his mother had been – for marrying a non-Quaker.
In December 1840 the couple sailed from Gravesend on the New Zealand Company ship Olympus as cabin passengers; they arrived in Wellington, New Zealand, on 20 April 1841. Thomas Mason bought a section at Taita, where, except for one short interval, the Masons lived for the rest of their lives, bringing up seven sons and three daughters (a fourth daughter and two sons died in infancy).
Around November 1841 a party of about 30 Ngati Rangatahi came from Porirua and settled on land Thomas Mason had begun to cultivate. The resulting dispute was resolved by the commissioner of native reserves, who negotiated an agreement whereby the Maori cultivated elsewhere. By April 1842 the tension had eased. Mason cleared the land and planted potatoes, seeds for other crops and seeds of trees and shrubs.
Mason disliked the way central and local government handled relations with Maori. Concerned at the prospect of war and also with the state of his wife's health, he removed his family to Hobart, Van Diemen's Land (Tasmania), in 1845. There he rejoined the Quakers in 1847 and Jane was accepted into membership. He worked as a bookkeeper before starting a small school for Quaker children in 1849. In 1848 he had visited the Maori 'rebels' transported to Van Diemen's Land, and by his own account helped to procure their release.
On 6 March 1851 the family returned to Taita. They resumed possession of their land, built a substantial house, and established an orchard of 150 fruit trees brought back from Van Diemen's Land. A stock of eucalypt seed was used for shelter trees, and the property became known as The Gums.
At the end of 1854 Thomas Mason had 30 acres of wheat and oats and 18 cows, but the following year the cleared land was sown in grass because pasture was more profitable. He had land at Mataikona in Wairarapa where he ran sheep and surplus cattle. By mid 1855 he had also secured 12,000 acres of run land at Maraekakaho in Hawke's Bay, and in 1858 a further 2,000 acres. The property was purchased over the period 1858 to 1866. Operation of the run was left to a manager for some years. The land eventually passed to his three younger sons and was later divided among them.
A surveying error had led to the house, woolshed and yards being erected on Maori-owned land. Mason paid rent and a charge for timber to Kurupo Te Moananui, until the Ngati Kahungunu leader's death in 1861. Te Hapuku, leader of Ngati Te Whatu-i-apiti, then tried to assert his ownership of the area rented. Demanding an additional back-payment of £300, he seized 2,000 sheep to enforce payment. Mason shifted all the buildings and yards to his own property and, following his Quaker principles, declined to allow force to be used to regain his flock. A few months later the sheep were returned.
Mason's capabilities led to his being asked to act with power of attorney for absentee owners and from 1868 to 1870 as agent of John Bridges, manager of the Wellington branch of the Bank of New Zealand. From 1854 he served in a succession of public offices. That year he was appointed to a board of commissioners to consider an education system for Wellington province and was made a justice of the peace. In 1855 he was one of the Hutt bridge toll committee. When the Hutt County Council was formed in 1877 he was for three years its first chairman. He was MHR for Hutt from 1879 to 1884 and supported the policies of the premier, Harry Atkinson, between 1883 and 1884. He became a member of the board of governors of the New Zealand Institute in 1877 and served as chairman from 1897 to 1902.
In his first plantings at Taita, Thomas Mason had started crop trials of potatoes of local varieties and from seeds he had brought with him. From his return in 1851 he began a programme of collection and acclimatisation of plants and trees that continued all his life. The resulting 12½-acre garden was said to be the finest in New Zealand. By 1871 he was tending 100 sorts of roses, 60 varieties of camellia and many azaleas and rhododendrons. When he listed his plants in 1896 there were 1,400 species, as well as many varieties of trees, shrubs and smaller plants and bulbs.
The public were able to visit and Mason was generous with gifts of flowers. He also gave seeds and cuttings to other gardeners. From 1877 to 1891 he was a member of the board of the Botanic Garden of Wellington, contributing much to the running of the garden and making substantial gifts of plants. When he died, the Taita property, which he had transferred to his daughter Elizabeth in 1885 and subsequently leased from her, passed through several hands. In 1922 the once-famous Mason's Gardens were subdivided and sold as building lots.
Thomas Mason was well known as 'Quaker Mason'. This was perhaps because of his use of Quaker forms of speech, his views on the bearing of arms, his regular holding of 'quiet meetings' at his home and the many prominent visiting Quakers who called or stayed. Jane Mason suffered from recurring ill health all her life; she died on 9 September 1900. Thomas Mason remained active until three weeks before his death at Taita on 11 June 1903. Both were buried in Taita cemetery.