This study analyses the impact of women leaders on environmental performance in a sample of 96 listed banks in the EMEA (Europe, Middle East and Africa) region from 2011 to 2016. Gender diversity in leadership positions is explored through women in the board of directors, chief executive officer gender, and the interaction between these two aspects. This study sheds light on inconsistent results in prior literature by testing three theoretical perspectives: gender difference, critical mass, and homophily. The main results suggest that there is nonlinear relationship between women directors and the environmental performance of banks and that female chief executive officers play a strategic role in shaping this relationship, by confirming the homophily perspective for the banking sector. Therefore, leader gender diversity is an important driver of environmental sustainability in banks, which are increasingly involved in environmental issues either directly, as companies, or indirectly, through their lending activity.