No transfer fee was disclosed but media reports said it was worth up to £4 million.
Nolan links up again with Sam Allardyce, his former boss at Newcastle and Bolton Wanderers, and will captain his new club who went down after finishing bottom of the Premier League last season.
The 28-year-old Nolan, who scored 12 goals last season, could be the ideal replacement for Footballer of the Year Scott Parker who is widely expected to leave the club in the close season.
"It's been a bit of a whirlwind but once I knew they wanted me, they have shown a certain hunger and desire to make sure I become a West Ham player," Nolan told the London club's website.
"Having the chance to link up with Sam again is a massive thing and obviously coming to such a massive club is great for me.
"I've come to West Ham because of the tradition of the club and everything about it. I've always enjoyed playing here and there was also the chance of linking up with Sam and working with him again," added Nolan.
"The be-all and end-all was this club wanted me and the owners put faith in me and have given me a security of contract. Now it's my time to repay them and hopefully I will do that."
Newcastle manager Alan Pardew, who used to be in charge at West Ham, waved Nolan off on good terms.
"I would like to thank Kevin for his sterling efforts as a player and captain of this club especially since I took over last season," said Pardew.
"He displayed admirable leadership qualities and I wish him every success at West Ham. It's a great club and I'm sure he will thrive there."
