He was sworn in as a lawyer on 14 December 1955. He began his career as a solicitor alongside the lawyer Albert Naud, known for having been
Pierre Laval's lawyer during the Purge. He inherited his legal library (which the latter had himself received from
Raymond Poincaré). He accompanied the social movement, alongside working peasants, miners, the
CFDT, activists fighting for the improvement of detention conditions - he denounced the conditions of detention in high security prisons and supporters of an
independent press. Henri Leclerc has defended famous clients, such as the newspaper
Libération, the mathematician
Alexandre Grothendieck,
Richard Roman,
Lucien Léger,
Dominique Strauss-Kahn (in the case that opposed him to
Tristane Banon then in the so-called Carlton case in Lille) and
Alain Lipietz, who was convicted of defamation. During the Jacques Tillier-Jacques Mesrine case in September 1979, the former having been left for dead at the bottom of a mushroom cellar, he defended one of the suspects, Charlie Bauer, who since 1977 has been granted parole, found a job as a bookseller and started a family. He discovers that his wife Renée Gindrat's account was checked as early as September two days before the identikit portrait inspired to the victim by a photo of Charlie Bauer and then questions Commissioner Mireille Ballestrazzi, who does not know why the OCRB did the financial research of September 13, which will allow her to obtain Bauer's acquittal at the trial in 1982, even if he is convicted of cannabis trafficking and receiving stolen property from part of a ransom from another kidnapping. He also defends Algerian independence activists, Breton autonomists and, after May 68, for years "leftists" being nicknamed at the time for this reason "the lawyer of the leftists". During the reconstruction for the Roman and Gentil affair, he is manhandled by the angry village crowd. He also acted as a civil party in the Omar Raddad case (representing the family of Ghislaine Marchal), represented the family of Pierre Overney, and defended the ex-boxer Christophe Dettinger, accused of intentional violence against police officers. He pleaded for the last time in 2020. == Death ==