Applying comparative historical methods, we employ and expand a political institutionalist analysis to explain agenda-setting, venue-shifting, and the timing of policy outcomes on same-sex marriage in the U.S., Canada, and Australia. Despite significant similarities across the three countries, Australia provides a unique counterpoint to the U.S. and Canada because it does not have a bill of rights, making litigation to obtain rights not enumerated in existing legislation unavailable to activists. Most research on lesbian and gay policy outcomes, particularly same-sex marriage, focuses on the role of the law, is based on single case studies, and does not address what happens when social movements cannot litigate for previously unenumerated rights. We utilize insights from social movement scholarship on transnational movements to build on and expand political and historical institutionalism by theorizing the role of international law. We demonstrate that the law continues to be important in Australia through the incorporation of international law into domestic institutions. Theoretically, we expand on political and historical institutionalism through our analysis of party discipline and international law to explain agenda setting, choice of venues, and the timing of policy outcomes.
