Elizabeth Oman was born in Caithness, Scotland, probably sometime between 1840 and 1848, the elder daughter of George Oman and his wife, Eleanor Lannigan. She arrived in Auckland, New Zealand, around December 1853 with her parents and sister Eleanor.
Little is known about her early life or education; her father worked as a labourer and the family appears to have lived in Onehunga at least from 1855 onwards. On 15 December 1875 at St Peter's Church, Onehunga, Elizabeth Oman married Michael Yates, a master mariner well known in the coastal trade. They lived in the family home at Selwyn Street with Elizabeth's widowed mother; there were no children of the marriage.
Michael Yates, a member of the Onehunga Borough Council since 1885, was elected mayor in 1888, holding office until 1892 when ill health led to his retirement. Elizabeth Yates assisted him with his duties throughout his incumbency. She was a strong supporter of women's suffrage and was the first woman to record her vote in the electorate under the new Electoral Act of 1893. She belonged to the Auckland Union Parliament and was a keen debater at its meetings.
In 1893 Elizabeth Yates accepted nomination for the office of mayor of Onehunga. She defeated her sole opponent, F. W. Court, at the election of 29 November, to become the first woman mayor in the British Empire. This radical departure from convention caused much comment throughout New Zealand and the empire, and Yates received congratulations from Premier Richard Seddon and Queen Victoria. The office also carried the appointment of justice of the peace. After being sworn in before Edward Conolly, judge of the Supreme Court, on 16 January 1894, she officiated occasionally as magistrate in cases involving women.
However, there was a hard core of local opposition to a woman filling these two traditionally male offices. Four councillors and the town clerk resigned immediately. Meetings were disrupted by unseemly altercations, and three councillors conducted an orchestrated policy of opposition to all proposals submitted by the mayor. Elizabeth Yates's tactless, dictatorial manner and partial disregard for established rules of procedure further exacerbated the situation. At times spectators crammed the small council chamber and interrupted proceedings, while outside the chamber unruly elements hooted and jeered. Newspapers published verbatim accounts of these 'disgraceful' scenes for the delectation of their readers.
On 28 November 1894 Mayor Yates was roundly defeated at the polls. Nevertheless, records show that much had been accomplished. She had liquidated the borough debt, established a sinking fund, reorganised the fire brigade, upgraded roads, footpaths and sanitation, and had personally lobbied the government to authorise the reopening of the Waikaraka cemetery. Even her enemies conceded that she had been an able administrator.
In September 1899 Elizabeth Yates made a triumphal return to the Onehunga Borough Council. She had lost none of her combativeness and was still forthright in expressing her opinions. She lost her seat in the election of April 1901.
Elizabeth Yates was admitted to Auckland Mental Hospital in November 1909 and died there on 6 September 1918. She was buried in St Peter's churchyard, Onehunga, beside her husband who had died in 1902. A pioneer in the participation of women in public life, Elizabeth Yates is assured of a place in the political history of New Zealand.