A deal was agreed to bring the Ecuador international from Pachuca earlier this month, pending the outcome of the hearing.
West Ham have subsequently announced that a decision has gone in their favour, and Valencia arrives at Upton Park on the back of an impressive World Cup campaign with his country.
Valencia scored all three of Ecuador's goals as they bowed out of the finals in Brazil at the group stage, and joins Sam Allardyce's side having also enjoyed a prolific spell with his previous club.
After joining Mexican side Pachuca from Emelec in his homeland, Valencia netted 18 goals in 23 Liga MX appearances.
The striker expressed his delight at officially becoming a West Ham player.
"I really appreciate the welcome I've been given and I'm excited to be here," he told West Ham TV.
"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.
"Of course, the World Cup gives me confidence to come to Europe and I want to take and advance with this opportunity that West Ham have given to me.
"The Premier League is the top league and I have followed it in Mexico. Obviously my countryman Antonio Valencia [the Manchester United winger] has played here for a long time so it's a big step for me to come here from Mexico and I hope I can be as successful as Antonio.
"It's exciting to be here in England and London. I want to repay the club in my performances for what they are investing in me and I'm really looking forward to it."
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