Hammers boss Sam Allardyce had already seen two bids for the England international rejected but has now got his man for an undisclosed fee, believed to be in the region of ?10.75million.
The 26-year-old is available for West Ham's Premier League game at Swansea on Saturday.
Speaking ahead of the move on Thursday, Allardyce claimed he was signing "one of the best final-third crossers in the Premier League".
Jarvis, who has three years of top flight experience with Wolves, is looking forward to playing for West Ham.
"I'm delighted to have signed," he told the club's official website.
"It's a fantastic club and I'm pleased to be here. It's a great club and it's got great history and tradition. I know about Bobby Moore and the history and tradition that go with that.
"I'll be playing with some fantastic players and it'll be great to get into training and I'm looking forward to playing with them. Hopefully I will add a bit of pace, crossing and deliveries that will provide some assists."
The former Gillingham man is likely to be involved at the Liberty Stadium and he is keen to start as he means to go on.
He said: "I've been told about how good the fans are hopefully they'll get behind me and I can show them what I can do.
"It'll be straight in and hit the ground running. There's no time to think about it, you've just got to get on with it, which is good. I hope to train with the team today and then travel up to Swansea."
