Messi has signed a two-year contract with the option of a further year after bringing an end to his 21-year stay at Barcelona.
Mbappe has just one year remaining on his contract in the French capital and has been linked with a move to Real Madrid.
PSG risk losing Mbappe for free next summer if the 22-year-old France international does not sign a new contract.
But Di Maria is adamant the inclusion of Messi means there is no better place for Mbappe to achieve his objectives, which includes winning the UEFA Champions League for the first time.
"Mbappe? I think he stays," Di Maria told ESPN.
"It's obvious that he's a player that all the big teams want but with the team that PSG has now, I don't think he's going to leave. I don't think he will find a better team anywhere."
The former Real Madrid and Manchester United winger added on Messi’s arrival: “I’m more than happy.”
“Everything I dreamed about happened in one month; winning the Copa [America] and being able to play with Leo in the same team. It’s what I’ve always wanted.”
