jats:titleAbstract</jats:title>jats:pThe Great Reform Act of 1832 was a watershed for democracy in Great Britain. We study the vote on 22 March 1831 in the House of Commons to test three competing theories of democratization: public opinion, political expedience, and threat of revolution. Peaceful agitation and mass-support for reform played an important role. Political expedience also motivated some members of Parliament to support the reform, especially if they were elected in constituencies located in counties that would gain seats. Violent unrest in urban but not in rural areas had some influence on the members of Parliament. Counterfactual scenarios suggest that the reform bill would not have obtained a majority in the House of Commons in the absence of these factors.</jats:p>