Mohamed Diame will become a West Ham United player on 1st July after agreeing a three-year contract at Upton Park.
The Senegal midfielder will move as a free agent at the beginning of next month when his deal ends with Wigan Athletic, who will be the newly-promoted Hammers' Premier League rivals.
Diame had been linked with a number of top-flight clubs and held talks with Liverpool before the sacking of Kenny Dalglish.
But West Ham boss Sam Allardyce won the race and Diame will be the third new face to arrive this summer after Stephen Henderson and Jussi Jaaskelainen.
The 25-year-old told his new club's official website: "I'm very happy and very excited to have joined the club and I'm looking forward to the start of the season.
"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."
Diame will compete with the likes of Kevin Nolan, Gary O'Neil, Jack Collison and Mark Noble for a place in the heart of Championship play-off winners West Ham's midfield.
Allardyce will have to decide who will be his first-choice selections but he has no doubt his latest acquisition will prove a great signing.
The West Ham boss said: "His potential is really good and he's ready to go and compete in the first team straight away, as he's had three years in the Premier League already.
"He's 25 and can only get better and I hope he can go on to prove that to me and all of the West Ham United fans. He will be a very exciting addition to the squad."
West Ham co-chairman David Gold also confirmed the deal on his personal Twitter account on Wednesday lunchtime.
"I am pleased to announce that we have just signed the Wigan midfielder 25 year old Mohamed Diame on a 3 yr contract," said Gold.