After a three-day trial, a jury convicted Vincent Madoure of taking part in the murder of Carl Davies, a 33-year-old former Royal Marines Commando.
Davies was found battered to death in a gutter on November 9, 2011. He suffered a fractured skull, broken bones, multiple bruising and cuts, an autopsy found.
He had arrived on the island two days earlier aboard a merchant vessel where he was working as a security guard.
Authorities only started to make headway in their investigation after a violent gang operating near the venue was arrested the following year.
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Three of its members were charged with Davies's death, two of whom were acquitted for lack of evidence -- a decision that the lawyer for Davies's relatives lashed as a judicial error.
His family was in court for the trial. Madoure, who maintained he was innocent of the crime, will file an appeal, his lawyer Henri Moselle said.
Reunion was claimed by France in the mid-17th century and is one of the country's five overseas departments. It has the same administrative structure as departments, or counties, in metropolitan France.