Sarah Louise Mathew was baptised on 19 November 1805, at London, England. She was the daughter of Ann Constant Strange and her husband, Richard Mathew. She had two sisters and two brothers, one of whom, George Felton Mathew, was a friend of the poet John Keats. Well educated, intelligent and an avid reader, Sarah Mathew worked as a governess from 1822. In 1831 she sailed for New South Wales, Australia, to marry her cousin, Felton Mathew, who, in 1829, had taken up an appointment as assistant surveyor of roads and bridges in Sydney. Sarah and Felton Mathew were married in Sydney on 21 January 1832. All their children were stillborn.
From 1832 to 1840 the couple lived at Windsor, near Sydney. In 1835 Felton was appointed town surveyor, but changing colonial politics led him to accept, reluctantly, the post of acting surveyor general in New Zealand at the end of 1839. Felton sailed for New Zealand on the Herald in January 1840. Sarah made arrangements for the removal of Felton's equipment and their household belongings, and arrived at the Bay of Islands on the Westminster on 17 March.
Sarah lived on the ship, going ashore to explore, visit, and attend church. She met James and Sarah Clendon, Agnes and James Busby, Eliza and William Hobson, the Church Missionary Society families, and local Maori. Her impressions of the town and its inhabitants are vividly recorded in her diary.
On 18 April she accompanied her husband on board the cutter Ranger and with him explored the coast south to Whangarei, Mahurangi, Thames, Tamaki and the Waitemata Harbour, in search of a suitable site for the permanent capital of the new British colony. Although a portrait taken in 1845 shows Sarah Mathew as a composed, elegantly dressed, slightly haughty woman with appraising eyes, her diary reveals that she cheerfully endured the most primitive conditions as she went ashore investigating rivers and terrain. She and Felton returned to Paihia on 12 June 1840, where they shared a mission house for the next two months.
Sailing again to the Waitemata Harbour in September, on the Anna Watson, Sarah was one of the official party, and the only woman present when, on 18 September, the preliminary agreement was signed with Ngati Whatua leaders for the purchase of the site of Auckland. Her first Auckland home was a group of tents in Official Bay, supplanted later by an attractive house. While Felton surveyed the town, Sarah recorded in her diary the progress of settlement in the new capital. In addition to maintaining the household with the help of her 12-year-old servant, she played a significant role in her husband's work. She transcribed and influenced his detailed reports, and was socially invaluable to him. Sarah and Felton Mathew were at the centre of social life in the settlement, entertaining Lieutenant Governor Hobson on his frequent visits to Auckland before he moved there permanently. Hobson, Sarah wrote, made their tent 'his home, his Office and everything else'. The difficulties of entertaining in such conditions were alleviated by the assistance of local Maori, who sold Sarah food, and later built the Mathews a raupo dwelling.
In 1845, as Felton's appointment, initially temporary, had still not been officially confirmed, he and Sarah went to England to clarify his position. On their return to New Zealand in March 1847 further difficulties with Governor George Grey caused them to sell their possessions and their house, and sail for England in September 1847. Felton, ill when they left, died ashore at Lima, Peru, on 26 November. Sarah continued on to England, where she later lived near Seaford, Sussex. In 1848 she applied, unsuccessfully, to the British government for compensation for perceived injustices her husband had suffered.
In 1858 Sarah Mathew returned to Auckland to look after her property interests. Her letters of this time express regret that she had missed the boom years of 1843–54, and her disappointment that, in spite of immigration, land was difficult to sell. She returned to England permanently in 1861. In the early 1870s she wrote her autobiography. She died at Tonbridge, Kent, on 14 December 1890.
Sarah Mathew adapted herself with enthusiasm and a perceptive eye to her new environment in New Zealand. A very close companion to her husband, she accompanied him on most of his expeditions. Her journals, letters and autobiography, through their clear observation and lively expression, give an authoritative insight into the complexities of colonial life and the early development of Auckland.