West Ham boss Alan Curbishley has made Luis Boa Morte his first signing at Upton Park in the club's bid to avoid relegation from the Premiership this season.
Boa Morte, the 29-year-old Portugal winger who had been valued at around £5million, has signed from Fulham for an undisclosed fee.
After arriving from Southampton in 2000, Boa Morte had remained at Craven Cottage despite being regularly linked to other clubs.
He will go into the squad for the FA Cup clash against Brighton tomorrow before the Hammers continue their bid for survival, and their next league clash is against Fulham.
West Ham confirmed on their club website that Boa Morte, who was Fulham skipper, agreed a three-and-a-half year deal with the club.
Curbishley had identified a need for commitment and hunger following the 6-0 thrashing at Reading on New Year's Day, which was the club's third defeat in a row.
After taking over from Alan Pardew, Curbishley's first match resulted in victory over Manchester United but they have not won since and he has highlighted the need for experience.
'I'm very pleased that we have been able to get the deal done so quickly,' said Curbishley on official website. 'I like players who are versatile, and Luis can play on the left, on the right, through the middle as a centre-forward, and even as an attacking midfielder.
'He is also very experienced, which is something I think we need and have been endeavouring to bring in. We have some very exciting young players, but I just felt we needed more experience in certain areas to help them out.
'The signing also puts other players under pressure, and that is what football is all about. Luis has great pace, a fantastic left foot, and he makes and scores goals. He is also very much a team player, and I am delighted to have got him.
'We are currently juggling a lot of balls in terms of the players we have targeted in this transfer window, and they haven't all come down yet, but this is a good start and I am sure Luis will make a big impact for us.'
Fulham boss Chris Coleman did not want to stand in Boa Morte's way after the winger revealed he wanted to move.
'I am of course disappointed that Luis has decided his future is not with Fulham. He has been a great servant to the club and we all wish him well,' said Coleman on club website fulhamfc.com.
'However, I have always said that if a player is not happy playing for this club and expresses a desire to go, then I would be prepared to let him leave; and this was the case with Luis.
'Having discussed this with the chairman and the managing director, we believe it is in the best interest of the club to invest in players who are prepared to commit their future to us.
'We will continue to add strength and depth this window and, if necessary, the next to ensure that we have a strong enough squad of players for the future to enable us to push on as a club, which remains our ambition.'