ABSTRACTThis study offers a new perspective on the development of political parties in the Australian House of Representatives. We analyse a data set of 3060 legislative votes to estimate how parties influenced the behaviour of 287 legislators who served in the first 12 parliaments (1901-31). We show that the socialisation of members and cohort replacement effects, as well as a decline in private member business and committee votes, explain why partisanship increased over time. Our results challenge two widely held beliefs about the organisation of political parties in the legislative arena and the Australian party system. First, the analysis demonstrates that the government’s ability to increase party discipline through control of the legislative agenda is limited when parliament is engaged in nation-building projects. Second, our study suggests that introducing restrictive parliamentary procedures played a role in consolidating Australia’s unique two-party system, which opposes Labor to the Liberal–National coalition.