Our study examines whether gender-diverse engagement partners constrain unethical earnings management behavior in a French mandatory joint audit setting. The investigation of the joint audit setting, by raising concerns about audit team organization and management, provides new insights into how gender-diverse audit partners contribute to the effectiveness of audit decision-making, resulting in reduced earnings management. The need for effective collaboration and communication between joint auditors may foster a transformational leadership style on the part of audit engagement partners. In this regard, we argue that better interaction between male and female lead audit partners confers a comparative advantage on gender-diverse audit partners compared to all-male audit partners. In line with our expectation, our empirical results show that gender-diverse audit partners are negatively associated with discretionary accruals of client firms. Gender-diverse audit partners are also found to constrain earnings management irrespective of whether clients hire one or two brand-name audit firms. Finally, we find that the pervasiveness of earnings management declines when client firms switch from all-male audit partners to gender-diverse audit partners. Our findings underline the importance of considering audit partner gender by policy makers in contexts where joint audits are required or in countries that are considering introducing joint audits.