Diamanti will join the Hammers for an undisclosed fee and has signed a five-year deal.
“I am very happy to be at West Ham United and to get the chance to play for Gianfranco Zola,” Diamanti told the club’s official website.
“This is a big club and I want to give everything for the supporters.
“I chose West Ham because the club has the tradition of playing great football.
“Also because the West Ham fans are really passionate and that is the way I am.”
