She joined the Canadian Suffrage Association in 1906 when it was founded by Augusta Stowe-Gullen and became an active member and campaigner.

[4] She served as president of the Canadian Suffrage Association from 1911 to 1914, until her controversial support for the militant tactics of the Women’s Social and Political Union in England resulted in her forced resignation.

[3] Denison encouraged women to imagine how they might create a different society, and promoted the creation of child care centers for poor working families.

[4] She argued that women's freedom would require them to gain financial independence from men and advocated against the gendered division of labor in society.

[11] She also corresponded about the women's vote with Ontario Premier James Whitney and Canadian Prime Minister Robert Borden.