This article investigates how class of origin and intergenerational social mobility impact left-wing party support among new and old core left-wing electorates in the context of post-industrial electoral realignment and occupational transformation. We investigate the remaining legacy of political socialization in class of origin across generations of voters in the UK, Germany and Switzerland. We demonstrate that part of the contemporary middle-class left-wing support is a legacy of socialization under industrial class–party alignments, as many individuals from working-class backgrounds – traditional left-wing constituencies – have a different (post-industrial) class location than their parents. These enduring effects of production worker roots are weaker among younger generations and in more realigned contexts. Our findings imply that exclusively considering respondents' destination class underestimates the relevance of political socialization in class of origin, thereby overestimating electoral realignment. However, these past industrial alignments are currently unparalleled, as newer left-wing constituencies do not (yet) demonstrate similar legacies.