[5] In 2003, he chose to return to Le Havre and joined with his father to co-manage the family insurance firm AXA.

In 2015, he was elected to the departmental council of Seine-Maritime (6th canton of Le Havre) in tandem with Christelle Msica Guerout.

Following the appointment of Édouard Philippe as Prime Minister, Luc Lemonnier was elected mayor of Le Havre on May 28, 2017.

[7][12] He also succeeded him as president of the urban community of Le Havre on June 25, 2017 as well as at the Metropolitan centre of the Seine Estuary.

[14] In January 2018, he expressed his doubts about the renewal of his membership in LR, indicating that he had not “had good signs since the appointment of Laurent Wauquiez".