Political marriage is an under-investigated form of social capital for family firms. In this study, we examine the relationship between political marriage and the growth of family firms. We analyze this relationship using survey data from parent–child dyads of 164 family firms in mainland China, along with qualitative data from eight semi-structured interviews. Drawing on social capital theory and self-verification theory, we propose that political marriage makes a significant contribution to the growth of family firms. We further propose that the effects of a political marriage on firm growth are moderated by the duration of the marriage and the degree of romantic love experienced by the couples. We find that the positive relationship between political marriage and firm growth is stronger when the duration of the marriage is longer. Our results also reveal a three-way interaction effect of political marriage, length of marriage, and romantic love on firm growth. In this interaction, the positive effect of political marriage is strongest when the marriage is long and the degree of romantic love is low (rather than high). Theoretical and practical implications are discussed.