Barthez has signed a two-year contract to keep him at Marseille until summer 2006.
'We have signed a contract for two years,' Marseille president Christophe Bouchet told his club's website. 'It's a good length. It leads up to the (2006) World Cup.'
Barthez previously played for Marseille between 1992 and 1995, and has impressed his new bosses.
'He has demonstrated that he really is one of the best goalkeepers in the world,' Bouchet added.
Marseille are sixth in the French League and they host Newcastle on May 6 in the second leg of their UEFA Cup semi-final with the tie goalless after the first leg.