While politicians are commonly depicted as having strong incentives to be responsive to both interest groups and citizens to govern and maintain office, the literature lacks designs that allow for assessing the causal effect of both types of actors on individual policy-makers. This study addresses this gap by formulating theoretical propositions regarding responsiveness of politicians to both public opinion and interest groups and testing them in a vignette experiment with responses from over 2000 Danish and Dutch local, regional and national elected representatives. Our study finds important differences in the dynamics of responsiveness to the two types of actors: Public opinion has a strong direct effect on the intended voting behaviour of politicians, whereas the effects of interest groups are weaker and mainly demonstrate the potential to influence the views of ideologically aligned legislators. Left-wing politicians, in particular, are responsive to civil society groups. These results have implications for understanding political representation and the role of interest groups across multiple levels of government. While the heightened sensitivity of politicians to some aligned groups creates a risk of policy-making biases, it is reassuring that interest groups have a weaker effect than public opinion and primarily hold potential to influence like-minded politicians.