Political scientists have long been interested in studying the elective office-holding of disadvantaged groups. However, this line of research primarily focuses on the representation of ethnic minorities in the U.S. Congress and identifies three types of determinants of minority candidates' electoral success: the demographic and political make-up of constituents, candidates' personal traits, and macro-level electoral rules. Much less attention is given to minority candidates' electoral success in statehouses. In this paper, we ask: what factors promote the electoral success of minority candidates in state legislatures? Beyond voter characteristics and electoral rules, we attribute minority candidates' electoral success to the social capital possessed by their in-group constituents. We theorize that social capital manifested as civic engagement and social connectedness, can become political capital for minority candidates. Using the Current Population Surveys Civic Engagement Supplement, we validate state-level measures of social capital by race and ethnicity. Linking group social capital to state legislative election outcomes, we find the stock of minority social capital contributes to the electoral success of minority candidates, while white social capital decreases minority candidates' electoral success. Key findings suggest social capital is a form of political capital for disadvantaged groups with private benefits for in-group candidates.