Ann West was born at New Scone, Perthshire, Scotland, on 17 May 1825, the daughter of Mary Brough and her husband, John West, a cotton handloom weaver. Ann may also have worked as a weaver before migrating to the Victorian goldfields in Australia. She was described as a house servant when she married a fellow Scot, James Robertson, in Melbourne on 8 August 1853. It seems that four children were born to the couple in Australia, three of whom survived infancy.
In August 1863 James Robertson enlisted for military service in New Zealand and with his family arrived in Auckland in February 1864 on the Thomas Fletcher. He was posted to Tauranga, where he was later joined by his family. Two daughters may have been born there. At some stage Ann Robertson had to assume the duty of supporting her family, and by September 1872 she was involved in the Tauranga accommodation business; until late 1879 she ran the Union Boarding House.
Ann Robertson and her family moved to Rotorua in February 1880, where she entered into an agreement to purchase the Ohinemutu (later Lake House) Hotel from Isaac Wilson. On taking possession of the hotel she faced an immediate challenge from prominent businessman Robert Graham concerning Wilson's legal ownership. Robertson and her daughters were physically ejected, and despite complex legal arguments she lost all rights to the hotel and forfeited £205 already paid to Wilson. Ann Robertson's determined stand gained her widespread sympathy. The affair also precipitated prolonged disputes within both the Maori and non-Maori communities concerning the occupation and leasing of Maori land outside the officially declared township of Rotorua.
Further disaster followed when Ann Robertson's occupation of a property on which she had established a thriving bakery was declared illegal under the terms of the Thermal-Springs Districts Act 1881. She was forced to abandon it, and this, together with accrued legal debts, resulted in her bankruptcy.
In September 1884 Robertson and 121 of her supporters petitioned Parliament praying for redress for injuries received from Robert Graham and losses sustained with the implementation of the Thermal-Springs Districts Act. Initially rejected, her petition was re-presented in succeeding years. In support of her plea she travelled alone to Wellington and is reputed to have been the first woman ever to address the House of Representatives. In 1892 the government granted her a gratuity of £300, the lease of various sections in Rotorua township and a 40-acre estate on the town's outskirts; she sub-let these properties. Ann Robertson then devoted her energies to providing a centre for the Rotorua Presbyterian community; she laid the foundation stone of St John's Presbyterian Church on 31 October 1896.
James Robertson died on 4 October 1897. Ann's fortunes had improved because of the grant of land, and she enjoyed a degree of leisure she had seldom known. She visited Scotland in 1895 and in 1912, when she also stopped at Palestine. She died at her residence in Haupapa Street, Rotorua, on 14 December 1922, and was buried beside her husband in the Rotorua cemetery.