Ms Toscan du Plantier’s badly beaten body was discovered by neighbours in a laneway near her holiday home in Schull, County Cork, on 23 December 1996.
Nobody has ever been charged in Ireland in connection with the 39-year-old’s death.
Bailey, who lived two miles away, was twice arrested for questioning by gardaí (Irish police) but released without charge.
The murder, and subsequent investigation, has received significant media attention in the years following Ms Toscan du Plantier’s death, becoming a notorious and protracted case of unsolved murder.
He denied any involvement in Ms Toscan du Plantier’s murder and, as he was not present in court for the French proceedings, he could not appeal the verdict.
Ireland’s High Court blocked his extradition to France, where the law allows suspects to be tried for murdering French citizens abroad, on multiple occasions.