New parties can shake up party systems by advancing new issues, influencing established competitors and affecting the dynamics of party competition. However, which kinds of new parties are successful? While the literature has extensively focused on institutional-level and election-level drivers of new party success, the literature on party-level determinants of new party success is scarce. As most studies on new party success focus on party entry at the election level or on new party survival, we argue that these studies suffer from selection bias as they do not leverage information on unsuccessful parties. This is understandable, since quality data on unsuccessful parties’ vote shares, party organizations and ideological characteristics are scant. To overcome this limitation, we examine the party-level determinants of new party success in the Netherlands, including all parties that have participated in national parliamentary elections since 1946. Our findings have important implications for the study of new parties in modern democracies.