He was born on 22 March 1934 in Sassandra, Côte d'Ivoire and received an education as an agricultural engineer at The Hague's Institute of Social Studies.
After President Christophe Soglo displayed a bias for northerners, Mensah opted to resign his post and traveled abroad.
He became a regional representative of the United Nations Food and Agriculture Organization in 1967, and became its assistant director-general in Africa three years later.
[2] Benin experienced a political liberalization in 1991, and Mensah opted to run for president that year on the Alliance pour le Renouveau Civique party.
In 2008, President Boni Yayi appointed Mensah to lead the High Commission for Concerted Governance.