The 28-year-old Scottish international has signed a three-and-a-half year contract to become Alan Curbishley's second signing of the January transfer window.
The Hammers' new boss is hoping Quashie, who has already been relegated from the Premiership with no less than four teams, will provide competition for places in the centre of midfield.
“We've signed Nigel because he is an experienced player who will add competition to our central midfield positions.” explained Curbs. “I saw that Mark Noble was also capable of providing that for us on Saturday, and it now means we have beefed up that area of the team.
”Nigel comes in here - like Luis Boa Morte - knowing full well the position we are in, and he is confident and convinced that we will be able to get out of the bottom three.”
Quashie himself has expressed delight at securing a move to a club he believes can move on to bigger and better things in the future. “I'm delighted that the deal has now been done and it feels great to be a West Ham United player.
“I'm now looking forward to being a part of the Club, getting out on the pitch, and getting my foot in to try and help us out of this position.
”As soon as I heard that West Ham were interested, I thought to myself: “I'd like to be a part of that”. Having met Alan Curbishley and the Chairman, I can see the direction the Club is going in, and I fully believe that the squad here is capable of achieving the success they want.”