The pair confirmed their engagement back in April, and have been tipped to tie the knot on August 11, the same date as Pitt's parents' golden wedding anniversary.
Bill and Jane Pitt have arrived at the couple's French chateau, as well as jeweller Robert Procop, who designed Jolie's engagement ring, reports The Sun.
The party is officially said to be for the actor's parents' wedding anniversary, but local residents claim that it will actually be a double celebration.
A source said: "Brad flew in to oversee preparations but they're all here now. They say it's for Jane and Bill, but some think this could be it. Even Angelina's private jeweller is here."
George Clooney has also been rumoured to have flown out to the chateau to join the couple for their wedding, which will only have a small guest list.
"George and Brad are best pals, there's no way he'd miss it," the insider said.
"He's at his house in Italy, but could fly to Marseille in an hour. There's a real buzz around the estate."
Pitt was recently reported to have bought Jolie a watch worth £250,000 ($389,652) for their wedding.