Fellow English Premier League rival have fended off competition from Arsenal, Liverpool and Manchester City to wrap up a deal for Cheikhou Kouyate.
The 24-year-old has joined the Hammers for an undisclosed fee, although it is expected to be in the region of £7m and he has put pen to paper on a four-year deal.
Kouyate becomes Sam Allardyce’s second signing of the summer having already added Mauro Zarate to their attacking ranks.
Confirming the news, a club statement read: “West Ham United are delighted to confirm the transfer of Anderlecht midfielder Cheikhou Kouyate for an undisclosed fee.
The 24-year-old Senegal international arrives from the Belgian champions on a four-year deal and becomes the Hammers’ second new addition of the summer, following the signing of Argentine striker Mauro Zarate.
The Hammers had to fight off strong competition from clubs across Europe to land the services of Kouyate, who possesses extensive UEFA Champions League and UEFA Europa League experience from his time at Anderlecht.”
Kouyate also expressed his delight after signing and told the club’s official in-house TV channel West Ham TV: “I am very happy, because today West Ham have given me the chance to play in the Premier League. So I’m very happy to join such a club and that gives me great pleasure.
“I know a few players who were also at the club, [Carlos] Tevez, Demba [Ba], Andy Carroll, who was obviously here last season.
“West Ham are a team who are known and who are going to help me to progress. For my part, I’m going to try to do great things here and try to improve further still as a player.
“That I’m here now is thanks to the manager, because he went out of his way, leaving his holiday for me, so he has done everything he could for me to join the club.
“He, my advisers and agents helped me make the right decision and said West Ham was the ideal club for me, because as a kid I dreamed of playing in the Premier League and now it’s here that my dream has been realised.”