How do political predispositions shape the social relationships individuals create? To address these issues, we leverage the domain of online dating, in which we can observe people’s political identities and preferences before they express a partner preference, which is important for distinguishing choice homophily from induced homophily and convergence. Further, we theoretically distinguish between two types of political homophily: preference-based homophily and engagement-based homophily. We first conducted an experiment in which we randomized political characteristics in online dating profiles presented to participants. To demonstrate external validity, we also analyzed behavioral data from a novel dataset gathered from a large, national online dating community. In both datasets, we observe that people find those with similar political beliefs more desirable and are more likely to “match” with them compared to people with discordant opinions. Additionally, people select relationship partners with whom they have a shared level of interest and engagement in politics. We therefore provide the first causal evidence that pre-match political characteristics produce political homophily and potentially political inequality. Our results have important implications for the literatures on social networks and politics, political polarization, homophily, social stratification and inequality, and others.