This paper studies the impact of separation from marital and cohabiting relationships on political party preferences. Relying on longitudinal data (1999–2017) from the Swiss Household Panel, it examines to what extent differences in party preferences between partnered and separated individuals are the result of a selection effect (with individuals who separate having different party preferences prior to their separation compared with partnered individuals) or of a causal effect (with individuals changing their party preferences following separation). The analyses show that partnered individuals are significantly more likely to support a party with Christian values (the CVP) compared with separated individuals, and indicate that this is due to a selection effect. For populist right (SVP) voting, we find a causal effect of separation. Interestingly, the event of separation increases the likelihood of supporting the populist right SVP. While separated individuals are more likely to support the social democratic party (PSS) than married individuals, we do not find a significant selection or causal effect of separation on support for the PSS. Overall, our results confirm the relevance of taking a dynamic approach distinguishing selection and causal effects and reveal that the effect of separation on voters’ party choice is modest but significant.