Montpellier coach Didier Nourault is reported to have said: "Justin is exactly what we were looking for."
Because the Ospreys were unable to guarantee Marshall first-choice status is thought to be the reason he has decided on the move to join the French team.
Justin Marshall, who is an 81-Test veteran, had originally joined the Ospreys from Leeds Tykes back in April 2006 on a two-year deal, and he chose an option of a third year in 2007, which extended his term until the end of the 2008/9 season.
Marshall was rumoured to have been earning around £200,000 per year but his career with the Ospreys had become in doubt though last year after the club recruited Wales scrum-half Mike Phillips.
