Nurses need psychological resources (supervisor support), as well as formal support from their organizations, which help them combat the demands from work and home and be more thrive at work. Family supportive supervisor behaviors have been demonstrated above and beyond general levels of supervisor support in reducing work–family conflict and improving well-being. In line with this, first aim is to examine the effects of Covid-19 pandemic on nurses’ perceived family supportive supervisor behaviors, work-to-family conflict, psychological well-being, and thriving. Second aim is to test the effects of nurses’ perceived family supportive supervisor behaviors on their thriving through work-to-family conflict and psychological well-being. The study was designed as cross-sectional and analytical. A total of 511 nurses from Nigeria and Turkey participated in the study. Parametric tests and Structural Equation Analysis were employed to analyze the data. The scores of nurses’ perceived family supportive supervisor behaviors and thriving decreased during Covid-19 pandemic, while the scores of their work-to-family conflict increased significantly. Results confirmed the negative effects of Covid-19 pandemic on nurses. Furthermore, results showed that family supportive supervisor behaviors had positive effects on thriving by decreasing work-to-family conflict and increasing psychological well-being. This study is one of the very first study examining the effects of family supportive supervisor behaviors on nurses’ work-to-family conflict, psychological well-being and thriving. Results of this study indicate that nurses need family supportive supervisors to be more thrive at work. Therefore, formal family friendly policies and implications improving family supportive supervisor behaviors are recommended in organizations.