A supporter of women's suffrage she joined the Kensington branch of the Women's Social and Political Union (WSPU) in 1907. Soon afterwards she was sentenced to six weeks' imprisonment for taking part in a demonstration outside the House of Commons.
In 1908 she joined the Actresses' Franchise League. Other members included Elizabeth Robins, Kitty Marion, Sime Seruya, Edith Craig, Inez Bensusan, Ellen Terry, Lillah McCarthy, Sybil Thorndike, Vera Holme, Lena Ashwell, Christabel Marshall, Lily Langtry and Nina Boucicault.
Mayo was arrested in June 1909 and November 1910 for taking part in WSPU demonstrations but was both times discharged. In November 1911 she was imprisoned for three weeks after taking part in the window-smashing campaign.
From 1921 to 1926 she was organizing secretary of the Six Point Group of Great Britain, which focused on what she regarded as the six key issues for women: The six original specific aims were: (1) Satisfactory legislation on child assault; (2) Satisfactory legislation for the widowed mother; (3) Satisfactory legislation for the unmarried mother and her child; (4) Equal rights of guardianship for married parents; (5) Equal pay for teachers; (6) Equal opportunities for men and women in the civil service.
Winifred Mayo died in 1967.