The 31-year old Romanian defender and captain has signed a one-year deal on a free transfer with the Hammers with his Shakhtar contract set to expire on July 1.
Hammers boss Sam Allardyce was thrilled to bring in a player who has won 15 trophies over a decade in Ukraine whilst playing almost 90 times internationally.
"I'm hugely happy that we've got a player of his experience and character," Allardyce told West Ham's official website.
"He's been playing Champions League football this year and at the highest level for many years.
"Shakhtar had offered him a very good contract but his ambition was to come and try his abilities and skills in England.
"We certainly know he's got the ability and he's at an age where he's still capable of producing at 31. He speaks perfect English, which he taught himself, and that shows the discipline and character of the man.
"Discipline, character and ability are the three big things in the Premier League and, with a little bit of adjusting, we'll see him early on in the season giving hopefully his best performances for West Ham."