During this period, she performed her research work on public economics and macroeconomic analysis at the Fondation national des sciences politiques.

From 2000 to 2002, Mathilde Lemoine served as an economist and Secretary General at the Observatoire Français des Conjonctures Économiques (an independent and public economic think tank), presided by Jean-Paul Fitoussi.

From 2005 to the end of 2006, she served as Advisor for macroeconomics and tax affairs to the French Prime Minister Dominique de Villepin.

[8][9] Mathilde Lemoine participated in the Leading Group on Innovative Financing for Development as the French expert named by the governments of a 12-nation task force.

In 2014, she presided a working group for the think tank Terra Nova that produced a report entitled “Entering and Staying in the Workforce.” [11] Mathilde Lemoine is a member of the Scientific council of the Cité de l’économie et de la Monnaie, an initiative of the Bank of France to improve public knowledge of economics, especially for young people.