Luc-Marie Constant Gnacadja or simply Luc Gnacadja is a Beninese politician and architect. He was Executive Secretary of the United Nations Convention to Combat Desertification from 2007 to 2013.
Gnacadja served in the government of Benin as Minister of the Environment, Housing, and Urban Planning from June 1999 to February 2005 under long-time President Mathieu Kérékou. Due to major political changes taking place since 2005, particularly with President Kérékou barred from running again by a two-term limit and an age limit of 70 years for candidates, Gnacadja ran for president as the unique candidate of the Envol movement in the March 2006 presidential election, receiving 11th place and 0.68% of the vote in the first round.
In terms of ministerial authority, Luc Gnacadja represented Benin as the head of delegation to the UNCCD and at the UN Framework Convention on Climate Change (UNFCCC) and Convention on Biological Diversity (CBD) while serving as Minister.