["Journal of Organizational Behavior, EarlyView. ", "\nABSTRACT\nFamily‐supportive supervisor behaviors (FSSBs) have been widely recognized for helping employees navigate work–family demands. Yet, it remains unclear whether the benefits of FSSB extend beyond the workplace to enrich supervisors themselves and their partners at home. Drawing on work–family enrichment theory and family systems theory, we propose a spillover–crossover framework to examine how engaging in FSSB enhances supervisors' family role performance and, in turn, positively associates with their partners' family experiences. Using a weekly experience sampling method with data from dual‐earner couples, we find that FSSB is positively related to supervisors' family role performance via work–family interpersonal capitalization. This enhanced family role performance subsequently crosses over to improve partners' family role performance. Contrary to expectations, the relationship between FSSB and interpersonal capitalization is stronger when family harmony is low, suggesting a compensatory effect. By shifting the lens beyond employees, our study highlights the broader relational reach of FSSB and offers new insights into its cascading impact across work and family domains.\n"]