Unemployment affects not only the subjective well-being of the individual, but also that of the partner. Based on the life course perspective and the spillover-crossover-model, we examine the mediating role of relationship functioning for such crossover effects of partner’s unemployment on subjective well-being. We also test whether gender differences in the mechanism of relationship functioning can explain the larger overall crossover effects on women compared to men. We use data from the German Family Panel pairfam (2008/09-2018/19), which provide more direct and comprehensive measures of relationship functioning than previous research, and allow us to examine couples’ communication and interactions, their conflict styles and behaviors, relationship satisfaction, and perceived relationship instability as mediators. To analyze the impact of the partner’s transition to unemployment on subjective well-being, we use fixed effects panel regression models and the product method of mediation analysis to estimate the indirect effects of relationship functioning. The results show that a partner’s transition to unemployment has a negative impact on one’s own well-being. The effects are more pronounced for women than men which can be partly explained by gender-specific effects of the partner’s unemployment on various aspects of relationship functioning, rather than by differential effects of the latter on one’s own well-being.