Mary Macarthur, the daughter of John Macarthur and Anne Martin, was born in Glasgow on 13th August 1880. The couple had six children, but only three survived, all of them girls. Mary attended the local school and after editing the school magazine, decided she wanted to become a full-time writer.
In 1895 the family opened a drapery business in Ayr and Mary was taken on as a book-keeper. John Macarthur was a supporter of the Conservative Party and an opponent of trade unions and sent his daughter to observe a meeting of the Shop Assistants' Union.
Mary was converted to the cause of trade unions by a speech made by John Turner about how badly some workers were being treated by their employers. Mary became secretary of the Ayr branch and at socialist meeting in the town, she met and fell in love with Will Anderson, an active member of the Independent Labour Party.
In 1902 Mary became friends with Margaret Bondfield who encouraged her to attend the union's national conference. She later recalled: "I had written to welcome her into the Union, but, when she came to meet me at the station, I was overcome with the sense of a great event. Here was genius, allied to boundless enthusiasm and leadership of a high order, coming to build our little Union into a more effective instrument." Mary was eventually elected to the union's national executive. Mary's political activities created conflict with her father who had a strong hatred for socialism. Anderson proposed marriage but Mary decided to pursue a career instead, and in 1903 moved to London where she became Secretary of the Women's Trade Union League.
As well as her trade union activities, Macarthur was an active member of the Independent Labour Party in London where she worked closely with two other Scots, James Keir Hardie and Ramsay MacDonald. Macarthur was involved in the Exhibition of Sweated Industries in 1905 and the formation of the Anti-Sweating League in 1906. The following year she founded the Women Worker, a monthly newspaper for women trade unionists. Later it was transformed into a weekly with a circulation of about 20,000.
Angela V. John has argued: " Mary Macarthur is perhaps best known for founding the National Federation of Women Workers (NFWW) in 1906. She began as president, but then exchanged offices with Gertrude Tuckwell (1861–1951) to become general secretary. By the end of its first year the NFWW boasted seventeen branches in Scotland and England and about two thousand members. Mary Macarthur was especially concerned about the relationship between low wages and women's lack of organization."
Mary Macarthur was an inspirational figure and recruited many women into the movement. This included Dorothy Jewson and Susan Lawrence, who both went on to become Labour Party MPs. Active in the fight for the vote, she was totally opposed to those women in the NUWSS and the WSPU who were willing to accept the franchise being given to only certain categories of women. Macarthur believed that a limited franchise would disadvantage the working class and feared that it might act as a barrier against the granting of full adult suffrage. This made Macarthur unpopular with middle class suffragettes who saw limited suffrage as an important step in the struggle to win the vote.
Mary Macarthur sat on the executive of the Anti-Sweating League and gave evidence to the select committee on homework in 1908. Macarther also campaigned for a legal minimum wage. In the summer of 1911 she organized an estimated 2,000 women involved in twenty concurrent strikes in Bermondsey and other areas of London.
Will Anderson followed Macarthur down to London and the couple married on 21st September 1911. Their first child died at birth in 1913 but two years later a daughter, Anne Elizabeth, was born. Anderson was elected to the House of Commons to represent Sheffied Attercliffe in 1914 but was defeated in 1918. Macarthur also stood as a Labour candidate in Stourbridge, but like the others who opposed the First World War, she was defeated in the 1918 General Election.
Mary was devastated when Will Anderson died in the 1919 influenza epidemic. She continued her work with the Women's Trade Union League and played an important role in transforming it into the Women's section of the Trade Union Congress.
Mary Macarthur developed cancer in 1920 and after two unsuccessful operations died at home, 42 Woodstock Road, Golders Green on 1st January, 1921. She was cremated at Golders Green Crematorium three days later.