While young people’s electoral behaviour in voluntary voting systems has been extensively studied, we know little about this in compulsory systems. To investigate, we examine the drivers of voting, not voting and not registering of Generation Z youths in Australia, which has long had compulsory registration and voting. We argue that Gen-Z voters, abstainers (registered, but who do not vote) and unregistered will differ according to their socio-demographics, socio-political engagement and political attitudes, following a ‘hierarchy of disengagement’. Drawing on original survey data from around 1500 Gen-Z Australians, we find that non-voters are distinguished by their unemployment status, lower political interest and weaker faith in democracy. Among non-voters, the differences between abstainers and unregistered mostly relate to their socio-economic backgrounds. Finally, we show that the most common reason for voting is not to get fined, while almost a third of unregistered Gen-Z citizens attribute their behaviour to lack of knowledge.