Jessie Marguerite McAllan was born in Dublin, Ireland, probably sometime between 1855 and 1857. She was the daughter of John McAllan, a merchant; her mother's identity is unknown. No information survives about Jessie's early life. On 11 December 1875 she married Hugh Bellis Williamson, a mercantile clerk, in Dublin. Around two years later the couple settled in Wanganui, New Zealand, and the first of their four daughters, Lena, was born. From about 1879 Hugh Williamson ran a chemist shop in Victoria Avenue.
Jessie Williamson was a principal member of the Wanganui Women's Franchise League (later renamed the Wanganui Women's Political League), which was established in May 1893 to co-ordinate locally the campaign for women's suffrage. She was treasurer in 1896, and either president or secretary from 1897 until 1903. In 1895 she and two other league members formed a deputation to the premier, Richard Seddon, to discuss the need for equal participation by both sexes in the civil service and equal pay for women and men.
Williamson was also active nationally, and as the league's delegate was a founding member in 1896 of the National Council of Women of New Zealand (NCW). In her report back to the league she declared that it was an unqualified mistake to admit participation of men at the first meeting of the council 'as it proved an opportunity for those with an "axe to grind"…to air their views…all the humbug that had been talked had been by men.' At the 1897 NCW conference she was made recording secretary and appointed to the committee of reference for resolutions. After joining the NCW's regional finance committee, she became national treasurer from 1898.
An accomplished speaker, Jessie Williamson was noted for 'her enthusiasm, and shrewd common sense'. She had an attractive personality and was very popular. A fellow worker recalled that 'The real wit of the gathering was Mrs Williamson.…I have a clear picture of her merry face, amusing sallies and fluent Irish tongue. We all brightened up visibly when Mrs Williamson began to speak.' Her sense of humour was remarked upon most often and she was described as the Scobie Mackenzie of the women's parliament, after the witty Otago politician. In 1900 her photograph appeared on the cover of the White Ribbon with a caption describing her as 'one of the best-known and most widely-respected residents' of Wanganui.
Once the vote was won, the unity, visibility and optimism of the suffragists waned. By 1903 the Women's Political League was no longer meeting and the NCW was in decline. Williamson was one of the key women who kept much of the council's business going towards the end. She played a principal role in the last full conference at Napier in 1902, and in 1903, when the council was forced to limit itself to executive meetings only, was part of the six-woman deputation to Seddon on women's 'disabilities'.
At the 1902 conference, growing defensiveness became apparent – a symptom of the retreat of feminism in this period. Jessie Williamson argued that the council's objectives had been greatly misunderstood. Women who were alive to their responsibilities were called political women, and she was glad to be one of them. In a reversal of her earlier statements, she now claimed that there was no such thing as a woman's question; the aspirations of sisters and wives were of equal importance to brothers and husbands.
As well as organising on behalf of women, Williamson took an active interest in community welfare and the need for institutional reform. In 1896 she was appointed an official visitor to the female department of the Wanganui prison. She was struck forcibly by the state of the cells – 'inhuman places' – and the fact that women had little say in prison management. She also attempted to get herself nominated onto the local hospital board, believing that the involvement of women would remedy widespread dissatisfaction with welfare administration. She argued that the contemporary system of charitable aid encouraged pauperism and that women should serve on all local bodies dealing with relief distribution since this work was essentially domestic, and would be easily performed by women.
Despite Frances Stewart's success in gaining a seat on the board in 1897, it took Williamson three years to become the second Wanganui woman to do so. After making herself available to several borough and county councils, she was appointed to the Patea and Wanganui United Charitable Aid Board as a representative of the Wanganui Borough Council in 1900. In 1901 she petitioned Parliament for elective hospital boards. From 1902 until she resigned in March 1904 she represented the Marton Borough Council on the Wanganui Hospital Board.
With Margaret Bullock, Jessie Williamson was involved in the ongoing debate over the appalling conditions at Wanganui's Jubilee Home for the elderly. She was the only hospital board member who visited the home and urged a proper system of classification of residents, a complete change of management and the 'cultivation of a humanitarian spirit'.
Her other concerns included illegitimacy and parental responsibility. She had a strong belief in the need to protect the young from corruption. Williamson denounced the sexual double standard which put the burden of disgrace for illegitimate births on women, but not men, and argued that men should be forced to acknowledge their role. Her solutions included compelling every man to provide for his illegitimate children according to his means, and aiding the mother in establishing proof of paternity. Those children whose paternity could not be proved and who could not be cared for, should be brought up in cottage homes and trained by good men and women to be useful members of society.
While Jessie Williamson shared many of the interests of her feminist contemporaries, she was wary of the temperance movement. She believed in temperance in all things but especially language: 'The rabid statements made by some temperance reformers really got her back up'. During her time in Wanganui Williamson was a member of the local SPCA, she founded a female court of the Ancient Order of Foresters of Wellington, and she displayed a keen interest in the local organisation of the conservative opposition.
Around 1904 the family moved to Linwood, Christchurch, where Hugh Williamson continued as a chemist. Jessie Williamson spoke at that year's public NCW meeting at Christchurch which was called to discuss Seddon's memorandum on 'Child-life preservation'. In 1905 she attended the council's final three-day executive session there.
Jessie Williamson's daughters Ann and Mary married, and in about 1909 the remaining family moved to Hawera. Hugh set up business in High Street where another daughter, Sheila, also worked as a dentist. By 1919 the Williamsons were living in Remuera, Auckland, while Lena Williamson, a chemist, boarded at the Nurses' Home at Auckland Hospital.
Although Hugh had retired, Jessie became active once again on behalf of women. As a younger member of New Zealand's first wave of feminists, she was one of a handful of women, including Christina Henderson and Jessie Mackay, who provided a link to the new burst of activism. From 1916 to 1918 she attended meetings to form an Auckland branch of the revived NCW as a representative of the Civic League – a feminist organisation formed in 1913 to raise awareness of women's issues and support women's efforts to run for public office. She was a vice president of the new branch of the NCW from 1918 to 1919. She was also vice president of the Civic League in 1922 and from 1926 to 1928, and served on the executive from 1931 to 1932.
Hugh Williamson died on 23 March 1926. After a lifetime of public feminist activity, which intensified after her husband's death, Jessie Williamson died at her home in Epsom, on 26 July 1937.