We study the politicians and voters of the Sweden Democrats, a major populist radical-right party. Based on detailed administrative data, we present the first comprehensive account of which politicians are selected into such a party. Surveys show that politicians and voters of the Sweden Democrats share strong anti-establishment and anti-immigration attitudes that drastically set them apart from Sweden’s other parties. Searching for individual traits that link naturally to these attitudes, we classify the universe of Swedish politicians and voters by social and economic marginalization and exposure to immigration. Politicians from the Sweden Democrats overrepresent marginalized groups without strong attachments to the labor market or to traditional nuclear families, which instead are underrepresented among politicians in all other parties. Among voters, the Sweden Democrats have higher electoral support in precincts with higher shares of the same marginalized groups. We see the mobilization of the marginalized as an important driver of the party’s success. Finally, we uncover that Sweden-Democrat politicians score lower on a number of valence traits than other-party politicians. In sum, the rise of the Sweden Democrats raised political representation for marginalized groups, but this came at a valence cost.