International migration moves people from one state to another, making the question of transborder political participation a topical question. This study investigates the extent to which emigrants from three European countries (Poland, Belgium, and Finland) engage in politics in their country of origin, based on their involvement in politics in their country of residence. The study adopts the transnational simultaneity framework proposed by Tsuda (2012), which considers migrants' political engagement in both the residence and origin countries as interconnected processes. Additionally, the study examines the inclusiveness of the political system in the country of residence in terms of the level of democracy and migrant integration policies. Two competing hypotheses are proposed at the individual and macro-level. In accordance with the zero-sum relationship model, it is expected that if individuals have the opportunity to become more politically engaged in their country of residence and choose to do so, their engagement in country-of-origin politics will correspondingly weaken. In other words, the more democratic and favourable towards migrant political participation the country of residence is, the less engaged emigrants will be in country-of-origin politics, as they can pursue active citizenship in their immediate environment. In contrast, the positively reinforcing relationship model suggests that increased political engagement in one country leads to increased involvement in the other. Consequently, a competing hypothesis is formulated, proposing that political activity is cumulative, meaning that the right to participate in politics in the country of residence and its active utilization also support engagement in country-of-origin politics. The empirical analysis is based on a survey conducted among non-resident citizens of Belgium, Finland, and Poland, recruited through Facebook and Instagram. Country-level data on the level of democracy and migrant integration policies in the countries of residence are obtained from the V-Dem dataset and the Migrant Integration Policy Index (MIPEX).