The Cameroonian spent a year with Portsmouth after agreeing a one-year loan deal to join the south coast side from parent club Montpellier in 2004.
Mezague spent last season with League Two club Bury where he made seven appearances before joining French fifth division outfit Sporting Toulon Var.
The midfielder was part of the Cameroon side that reached the final of the 2003 Confederations Cup, in which team-mate Marc-Vivien Foe tragically died during the semi-finals.
Later that year Mezague was involved in a car crash that left him hospitalised and in a coma for three days.
His last club confirmed his passing: “It is with great sadness that Sporting Toulon informs you of the death of Valery Mezague.”
The cause of death is unknown, but a Toulon police source told AFP: “An autopsy will he held on Monday. We do not currently have any suspicions (of criminal activity).”
Mezague was born in Marseille but represented the country of his parents, although his international career was cut short after his car crash.
A promising, athletic youngster, he joined Sochaux in 2005 but the last five years of his club career were mostly spent in France’s lower leagues, with the exception of a season in Greece with Panetolikos.
Mezague’s younger brother Teddy currently plays for Belgian side Mouscron.
Valery Mezague during his time at Sochaux (Imago)