A court in France has found Ian Bailey, a British former journalist, guilty of murdering Sophie Toscan du Plantier, a French film-maker who was battered to death in Ireland.

The cour d’assises in Paris on Friday sentenced Bailey to 25 years for the brutal murder in west Cork in 1996, an infamous cold case that has confounded Irish authorities and divided public opinion over Bailey’s guilt or innocence.

Toscan du Plantier’s relatives embraced after the verdict was read out. Her only child, Pierre-Louis Baudey-Vignaud, hailed the ruling. “It is a victory for justice, it is a victory for the truth and now Ireland will have to extradite Ian Bailey.”

Bailey, 62, denies any involvement. He lives in Ireland and did not attend the week-long trial and was convicted in absentia. But the family of Toscan du Plantier, who was 39 when she was killed, are likely to see the conviction as long overdue and will hope it paves the way to potential extradition.

“All they’ve done is convict an innocent man who had nothing to do with the crime,” he told the Guardian, speaking from his cottage near Bantry, County Cork, minutes after the verdict was announced. “All they’ve got is a pyrrhic victory.”

He paraphrased some Beatles lyrics – “Have you heard the news today? Oh boy” – and said he was trying to keep his spirits high. “The sun has come out, I’m good,” he said.

The former freelancer, who used to run a small news agency in Cheltenham that supplied stories to the Sunday Times, had predicted he would be “bonfired” in Paris. He compared his limbo – he is notorious in Ireland yet has never been charged there – to medieval torture. His solicitor, Frank Buttimer, called the proceedings in Paris a “show trial”.

The conviction is expected to lead to a new French arrest warrant and renewed extradition attempt. Irish courts have rejected two previous attempts to extradite Bailey, citing flaws in the French requests.

Irish police identified Bailey as the prime suspect soon after Toscan du Plantier’s battered body was found outside her holiday cottage, three miles from his own cottage, on 23 December 1996.

He had cuts on his face and hands, a record of violence against his partner, Jules Thomas, and admitted to having left his cottage – to an adjacent shed to write an article, he said – on the night of the murder. However there was no forensic evidence linking Bailey to the scene and a key witness retracted testimony, saying police had improperly pressured her.

Irish prosecutors decided there was insufficient evidence to press charges.

French authorities transplanted the case to Paris, where it was heard by three judges. Under French law a person suspected of murdering a French citizen in another jurisdiction can be tried in France.

Baudey-Vignaud, the victim’s son, visited west Cork earlier this month to urge witnesses to testify, saying his mother was not a ghost. “She is the victim of human cruelty and violence which has no place here.”

He added: “Sophie fought like a lioness against the most atrocious violence there is … I can’t bear the thought of her blood seeping into your soil.”

The public prosecutor, Jean-Pierre Bonthoux, said the Irish prosecutor had examined the evidence on “a segmented basis” rather than in its entirety. “He concluded each segment was zero and when he added segment to segment, he was adding zero to zero and got zero rather than looking at the bigger picture.”

Bonthoux accused Bailey of cowardice and insulting the French justice system by failing to come to France. Bailey said he had no plans to leave west Cork.

A 13-part podcast titled West Cork has shone new light on the case. The director Jim Sheridan is making a documentary.