François Decoster is active on several levels - local, regional, national and international. Involved for nearly 25 years on the municipal level of his home town of Saint-Omer, in the Pas-de-Calais department, François Decoster began his political career as a municipal councillor from 2008 to 2014 and from 1997 to 2001, then as deputy mayor in charge of finance and economic development from 2001 to 2008. He became mayor in 2014. He joined the Nord-Pas-de-Calais regional council in 2010 and sat in the new Hauts-de-France region from 2016. Vice-president of the regional council, he was vice-president in charge of culture from 2016 to 2019 and regional languages and international relations since July 2021. Appointed since 2012 as a member of the European Committee of the Regions, he has held several responsibilities there, including the presidency of the Commission for Citizenship, Governance, Institutional and External Affairs, or CIVEX. Head of the French delegation to the Committee from 2017 to 2020, he has been President of the Renew Europe group within the Committee since February 2020.

Author of several reports on migration policies or institutional issues, he has worked in the political party Mouvement Démocrate, in the European Parliament and for 11 years in ministerial cabinets as technical advisor, diplomatic advisor, deputy director and then director of cabinet. His functions covered international areas such as cooperation policies, transport, education, higher education, research, space, French communities abroad, tourism, foreign trade and the French-speaking world. He sits on the boards of cultural institutions, including the Orchestre national de Lille since 2020 and is vice-president of the Louvre-Lens art museum. He teaches at the College of Europe in Bruges, Belgium, on European space policy, and has previously taught at Sciences-Po Paris and Lille, the University of Paris-Assas and the Higher Institute of Business in Beirut.