Payet has signed a five-year contract with a further one-year option for an undisclosed eight-figure fee.
The 28-year-old has explained why he made the switch from Marseille to West Ham.
“West Ham really showed me that they wanted me to come, both the Joint-Chairmen and the manager,” the former Nantes star told West Ham’s official website.
"That’s very important for me. I was also keen to sign up to a clear project. West Ham’s is very interesting and matches perfectly with my ambitions.
“Firstly I spoke with the manager, who really wished for me to come here and had been watching me a lot. He made it clear that he wanted me to sign and that too was important in my choice.”
Good signing for West Ham
The signing of Payet is a real statement of intent from West Ham, who have lofty ambitions for the future.
The Frenchman was one of the best players in Ligue 1 last season, helping Marseille finish fourth in the league table.
The former Lille star scored seven goals and created 134 chances in league appearances
The 28-year-old had a pass accuracy of 80% and a shot accuracy of 47%, and won three headers, 66 dribbles and 17 tackles.
Payer’s arrival at West Ham is going to make the London outfit real challengers for a top-six or top-eight finish in the Premier League next season.