Independent-minded and well-connected, Mary Hayden played an important role in educating the elite of the Irish Free State, and at the same time, she advocated for the interests of the underprivileged. Hayden was a professor for decades, emerging as a power broker in the university world. But perhaps even more importantly, she was a consistent feminist whose influence could be seen over many decades—culminating in her opposition to de Valera’s 1937 Constitution.