In the 2012 presidential election, Renson publicly endorsed the Socialist Party's candidate François Hollande.[1] Similarly, he voted for Socialist candidate Anne Hidalgo, a family friend, in the 2014 Paris municipal election.[2]
In 2017, Renson joined Emmanuel Macron's La République En Marche! party.[3] He was elected to the National Assembly in the legislative election later that year, as the MP for Paris's 13th constituency, defeating incumbent Jean-François Lamour of The Republicans party.[4] He took office on 21 June 2017. Renson was elected a week later by his peers to one of the six vice-presidencies of the National Assembly, a rare occurrence for a new member, a position in which he succeeded David Habib of the Socialist Party. He also serves on the Committee on Foreign Affairs. In addition to his committee assignments, he is a member of the French-Greek Parliamentary Friendship Group and the French-Lebanese Parliamentary Friendship Group.[5]
In late 2018, Renson, Aurélien Taché and Matthieu Orphelin convened a group of around 20 members of the LREM parliamentary group with a "wish to express a humanist, social and ecological sensibility and to better raise citizens' concerns"; the initiative was widely interpreted as the launch of a left-wing faction within the group.[6] In 2020, he joined forces with Barbara Pompili as co-founder of En Commun, a group of centre-left LREM politicians.[7]
Ahead of the 2020 Paris municipal election, Renson failed to win the party nomination for the mayorship against Benjamin Griveaux. He subsequently endorsed Cédric Villani, who also failed to win the nomination but decided to run as an Independent.[8]
In February 2022, Renson announced he would not seek reelection to a second term as an MP. In his announcement, he heavily criticised the lack of internal debate within the outgoing parliamentary majority, stating: "When we all think the same thing, it is because in reality we do not think anything".[9]