From 1995 to 1997, Lemoine served as deputy chief of staff of the Minister of Labor and Social Affairs Jacques Barrot in the government of Prime Minister Alain Juppé, in charge of coordinating reform of the national health insurance system and hospital reform.

At the same time he was a chargé de mission with the Secretary of State for Healthcare and the National Health Insurance system Hervé Gaymard.

In 1992 and 1993, Lemoine headed the Institut du Coeur of Hô Chi Minh-City, in Vietnam, for a year.

After the family controlled private equity group Wendel parted company with its chief executive Jean-Bernard Lafonta in 2009, Lemoine was appointed as his successor.

Ahead of the 2022 presidential elections, Lemoine publicly declared his support for Valérie Pécresse as the Republicans’ candidate and joined her campaign team.