The Premier League club confirmed the arrival of the 31 year-old on a three-year contract for an undisclosed fee on Friday, having earlier revealed they were on the brink of ''tying up a major new signing''.
Diarra said: "I am very happy to be here at West Ham - everything is signed now which is good and I am excited to be here at this club and to be playing for them in the Premier League.
"I know a lot about West Ham as a club, and when I knew they were interested in signing me, I was very happy and knew it would be a good choice for me.
"We are a Premier League club and I know of players who were here before like Paolo Di Canio and Scott Parker, but of the players now in the team, I know Guy [Demel], Mo [Diamé] and, of course, Modibo Maïga, who played in the French league last year.
"The club has just been promoted and I am looking forward to a good challenge with the team ahead. I see this as my chance in the Premier League to do well with West Ham. I hope that my experience can help and the fans will see me give my all in the matches."
Diarra is West Ham's eighth summer signing and there could be more to come. It is understood they want to buy Wolves winger Matt Jarvis and there were reports today they had seen a £9million bid turned down.
Diarra, meanwhile, was one of France's better performers at the European Championship, despite a disappointing season with Marseille.
He previously failed to make the grade at
His Marseille exit seemed inevitable when he reported back from Euro 2012 six days late and was fined €40,000.