The 25-year-old will complete the move to Upton Park on July 1, when his
current deal with Wigan runs out.
'I'm very happy and very excited to have joined the club, and I'm looking
forward to the start of the season,' Diame told West Ham's website.
'I know the fans here get behind the team all the time, and I'm looking
forward to showing everybody what I can do on the pitch.'
A Senegal international, Diame scored three goals in 26 Premiership matches
last term for Wigan, which finished in 15th place.