This article presents a comparative analysis of the legal regulation of political parties as competitors in, and as entrants to, the electoral contest. Laws that regulate ballot access and the registration of political parties as ‘official’ electoral actors are examined in four established common law democracies: Australia, Canada, New Zealand and the United Kingdom. The article explores the ways in which these regulations are used to control the degree of party competition in each system, and how some specific laws might privilege some parties (for example, incumbents) over others. Specifically, the article analyses the role that the courts play as interpreters and adjudicators of these laws in different constitutional contexts – shaping the contours of party competition and legitimate political activity based on their understandings of constitutional freedoms, effective elections and governance arrangements, and particular normative conceptions of the role of political parties in modern societies.