A French court has found Ian Bailey guilty of murder and sentenced him to 25 years in prison.
Judges have ordered a new arrest warrant to be issued.
The 62-year-old was accused of killing Sophie Toscan du Plantier in West Cork over 20 years ago.
She was found dead at her holiday home near Toormore on December 23rd 1996.
The French court charged Mr Bailey - a British former journalist who lives in Ireland - with voluntary homicide.
The case was heard in his absence, and he was convicted in absentia.
Mr Bailey has repeatedly denied that he had any involvement in the murder, or that he ever made any admissions in relation to her death.
The judges began their deliberations earlier after public prosecutor Jean Pierre Bonthoux spent 90 minutes summing up the indictment against Mr Bailey.
The conviction was welcomed by Ms Toscan du Plantier's family.
In comments quoted by The Guardian, her only son Pierre-Louis Baudey-Vignaud said: “It is a victory for justice, it is a victory for the truth and now Ireland will have to extradite Ian Bailey.”
Mr Bailey's solicitor Frank Buttimer, however, claimed the decision is a "grotesque miscarriage of justice".
He said: "[Mr Bailey] had expected it, but when it does happen it strikes you very, very badly. [He's had] the reaction of one who has been wrongly convicted of a crime which he has not committed.
"There wasn't a trial in the way that we know it. The so-called evidence... under no circumstances should have been admitted in any functioning criminal justice system."
Speaking ahead of today's verdict, Mr Bailey told the Irish Examiner that he remained "calm in the eye of the hurricane".
He added: "I'm in good company, and I've got a lot of support."