This paper examines how and why France and Belgium came to modify their respective constitutions and pass parity laws. The first section analyses French and Belgian women’s acquisition and exercise of political rights and, in particular, their right of eligibility. Statistics concerning women’s presence in both the lower and upper houses (France’s National Assembly and Senate and Belgium’s Chamber of Deputies and Senate) are used to assess the extent to which they have been able to exercise their right of eligibility. The second section focuses on the involvement of French and Belgian women’s movements and parties in the introduction of gender parity reforms, and the third section examines the involvement of French and Belgian executive and legislative elites in the adoption of constitutional reforms. Overall, it appears that in France, the women’s movement played the key role in the introduction of parity reforms whereas in Belgium, both the women’s movement and political parties did. Further, although in both countries top executive and legislative elites from the left and the right were actively involved in the ratification of constitutional reforms, their involvement appears to have been more collaborative in Belgium than in France.