Thomas' role was to find a suitable site for their proposed settlement, and what became the Canterbury region with Christchurch as its capital was the result of his efforts.

He was dismissed in early 1851 over quarrels with John Robert Godley, the agent of the Canterbury Association, just after the first settlers had arrived in the colony.

Having allowed for Hagley Park as a generous central city green space is regarded as his major achievement, and it is his lasting legacy.

[1] He served in India and in November 1827 transferred to the 19th (1st Yorkshire, North Riding) Regiment of Foot[2] for service in the West Indies.

Thomas left the army in 1833 with the rank of lieutenant, and worked in North and South America as a surveyor and mining engineer.

As the land proved to be unavailable, he ventured into fishing and whaling, but in 1841 accepted a survey position under William Mein Smith.

Thomas undertook work in Wanganui and Porirua, but together with most of his colleagues, he was sacked by chief surveyor Samuel Brees in March 1843.

[5] Thomas' remit included to find the site of the settlement anywhere in New Zealand, and it appears that the Canterbury Association expected that land in the Wairarapa be taken up, but he was instructed to obtain the consent of both the Governor (George Grey) and of Bishop Selwyn.

Thomas may have had preconceived ideas about the location of the desired settlement, as he mentioned to a Nelson settler that the question is about "Port Cooper or nothing", with the name referring to what is now known as Lyttelton.

Thomas himself explored Banks Peninsula on foot and went to Port Levy, Pigeon Bay, Akaroa, Little River and back via the inland shore of Lake Ellesmere / Te Waihora.

Fox reported the following to T. C. Harrington, the secretary of the New Zealand Company:[18] Mr Thomas not only concurred in these arrangements, but was anxious to have them entered into, believing, as I do, that the presence of Messrs Deans and Mr George Rhodes with their stock and farms and their knowledge of climate, seasons, etc., will prove most valuable to the Canterbury immigrants in the early days of the settlement.

[19] During May 1849, both the Bishop and the Governor gave their approvals of the settlement for the Canterbury Association,[20] and Grey thus confirmed that Port Cooper was not going to be part of the French land claim any longer.

To conform with his instructions, Thomas initially placed the settlement's capital at the head of Lyttelton Harbour / Whakaraupō at the present-day Teddington.

Godley was the agent for the Canterbury Association, and he put an immediate stop to the works, as available funds had been used up; instead, a walking track was built over the Port Hills that became known as the Bridle Path.