Do large franchise extensions bring about dramatic electoral changes? Electoral reforms in 1918 nearly tripled the number of people eligible to vote in Ireland. Following the reforms—the largest franchise extension in U.K. history—the previously obscure Sinn Féin party secured 73 of Ireland’s 105 seats, an outcome that precipitated a guerrilla war and ultimately independence from the United Kingdom. However, our analysis finds little evidence that the franchise reforms benefited Sinn Féin. New female electors appear less likely to have supported Sinn Féin while new male electors were no more likely to vote for Sinn Féin than the existing electorate. Women also appear less likely to have cast a vote at all. Economic and social factors did matter when it came to voting, however, as did public opinion in relation to armed rebellion. These results remind us that dramatic political changes, such as those that took place in Ireland 1918, do not require dramatic changes in political participation. Sinn Féin’s electoral success was more likely driven by a change of heart on behalf of the Irish electorate, rather than a change in its composition.