The 29-year-old midfielder has made five appearances for Didier Deschamps' France side and played 50 games for Serie A club Roma last season, scoring four goals with 10 assists.
Veretout returns to France after being sold to Premier League club Aston Villa by FC Nantes in 2015, having also played for Italian side Fiorentina.
Marseille finished second in Ligue 1 last season and qualified for the Champions League.