Mary Teresa Hayden (1862 – 12 July 1942) was an Irish historian, Irish-language activist and campaigner for women's causes.

She attended the Royal University of Ireland where she graduated with a BA (1885) and an MA (1887) in Modern Languages.

[1] A campaigner for gender equality and noted as a public speaker, she was a prominent member of the Dublin Women's Suffrage Association.

[2] Hayden worked with Mary Gwynn to establish the Irish Catholic Women's Suffrage Association (ICWSA) in 1915.

[3][4] She helped to form the Women's Social and Progressive League as a political party committed to opposing the 1937 Constitution of Ireland and any regressive consequences it would entail.