"We are very happy to welcome Andriy," West Ham director of football Mario Husillos said on the club's website.
"When we had the opportunity to sign him, we did not hesitate, because he really is the kind of player that we were looking for."
The London side did not disclose the fee for the 28-year-old, although British media reports said it was around 17.5 million pounds ($23.2 million).
The 28-year-old enjoyed a stellar spell at Ukraine's Dynamo Kiev where he scored 137 goals in all competitions since his making his senior debut in May 2008. He is the second highest goalscorer for the Ukranian national team after Andriy Shevchenko.
West Ham begin the new league campaign with a difficult away trip to Liverpool on Aug. 12.
(Reporting By Arnab Paul in Bengaluru; Editing by Christian Radnedge)
