Valencia, who scored all three of Ecuador's goals at the World Cup finals in Brazil, signed a five-year contract to join the east London club from Mexico's Pachuca earlier this month, subject to a successful work permit hearing.
"I've already watched and read a lot about the club to learn about it - I know the fans are really passionate and I'm really glad to have signed," Valencia told the club website (www.whufc.com).
"The World Cup was a good tournament for me personally. I scored three times and for my first World Cup it was a good experience, but I hope my next one is better for me and the team.
"Of course, the World Cup gives me confidence to come to Europe and I want to take (advantage of) this opportunity that West Ham have given to me."
West Ham open their league campaign at home to Tottenham Hotspur on Aug. 16.