[4] As a mayor, he strived to develop local facilities, at the level of the city, while associating himself with a series of metropolitan projects and intending to pay "particular attention to underprivileged neighborhoods, where unemployment can reach records”.

In charge of sanitation, he inherited several important files, including that of the cleanup of the Marque,[8] a river that notably crosses the towns of Marcq-en-Barœul and Marquette-lez-Lille.

These functions also led him to become at the same time administrator of the Agence de l'eau Artois-Picardie [fr] (1995-2001), then chairman of the program commission of this public institution (1998-2001).

[2] With the accumulation of mandates, he decided to give up his post of municipal councilor, leaving his chair as mayor to his first deputy, Bernard Gérard.

He was a rapporteur for a certain number of important bills, such as that on the creation of the Equal Opportunities and Anti-Discrimination Commission (HALDE)[11] or that relating to the prevention of delinquency.

[16] He was also a member of the boards of directors of the French Office for the Protection of Refugees and Stateless Persons (OFPRA) and the Conservatory of Coastal Spaces and Lakeshores.

[18] The debates around this bill have also been the occasion for disagreements between the Government (represented by Rachida Dati then Michèle Alliot-Marie) and the senatorial majority.

[19] With the support of his fellow senators in the Law Commission and then in the Joint Parity Court, Jean-René Lecerf succeeded in safeguarding the principle of individual confinement in particular.

Attentive to the progress of these cases and having had the opportunity to meet Francis Évrard during a visit to the prison of Sequedin, he revealed a certain number of avenues in order to fight against recidivism, including the obligation of care and medical monitoring.

[24][25] The technical relevance of this proposal had been the subject of criticism from various online media,[26][27][28] especially since its filing shortly preceded the demonstrations of vulnerability of the secure electronic chips of the English and German national cards.

"[30] Jean-René Lecerf left the Senate on 21 April 2015 to Patrick Masclet to devote himself to the presidency of the departmental council of Nord.