He was instrumental in the Wellington colony's early administration, the setting out of the town, and country acres, and later oversaw work in the Manawatu and Wanganui. He was gazetted as a magistrate. He also served on the short-lived Wellington Town Council established by the Company. His name survives today however only indirectly, in Mein Street, Wellington. His other contributions included helping to form the first library, designing the first light at the entrance to the harbour, exploring the route to Porirua and the Kapiti Coast, and founding the Horticultural Society. Though getting on the wrong side of Colonel Wakefield, the Company's Principal Agent, and being dismissed as Surveyor General from early 1842, when he was replaced without warning by Samuel Charles Brees, he was commissioned to sail down the East Coast of the South Island in September 1842 to help locate another site for settlement by the New Zealand Company. He was thus an early visitor to what is now Christchurch, Akaroa, Port Chalmers and Bluff, but was shipwrecked in the course of the return trip. He still had the opportunity to visit and name Quail Island in Lyttelton Harbour, after crossing the peninsula on foot, visiting whalers and Māori alike. Later he surveyed a number of other parts of the lower North Island, including some townships in Wairarapa, the coastline as far north as Castlepoint, and the Taratahi plain. He also spent time in the 1850s seeking a better route through the mountains to Wellington. He was involved in operating a farming venture near Wellington at Terawhiti until 1846. At about this time, he was responsible for establishing one of the earliest cattle and sheep runs in the Wairarapa, at Huangarua, near modern Martinborough, with his friend Samuel Revans in about 1845, when he seems to have left his first home under what is now Tinakori Hill, Wellington, driving some of the first cattle round the rocky coastline. They were among the first half dozen settlers in the valley. There he and Louisa raised their five children. He also carried on surveying and was a local magistrate and politician. He also had close dealings with local Māori, and his image is said to be preserved in one of the celebrated carved perimeter posts at Papawai marae, near Greytown.
He died in Greytown in the Wairarapa in 1869 after a lengthy illness, at his and Revan's home "Brierly" at Woodside. Louisa had died there two years earlier. One of his descendants, Philippa Mein Smith, is a historian and wrote a biography of Mein Smith for the Dictionary of New Zealand Biography in 1990.
