The 28-year-old signed a four-year deal at the London Stadium this week and is Manuel Pellegrini's fifth signing in this summer transfer window.
The winger, who has been capped 77 times for Ukraine, has now revealed his joy at joining a club of West Ham's stature. "I am happy to join West Ham United. West Ham is a big club with big fans," he told West Ham's official website.
"I cannot promise them [the fans] that I am the second [Lionel] Messi, but I can promise one thing, which is that I will be giving them my all on the football pitch".
Yarmolenko also revealed that he came to England with the hope of winning trophies in east London, having previously experienced lifting the Ukrainian Premier League with Dynamo Kiev before opening up on his difficult year long stint in the Bundesliga with Dortmund.
"I will give all my energy to do everything for the team to win games. I will give my all to help the team to win as many matches as possible and, with any luck, to win trophies too".
"Personally, my year with Borussia Dortmund turned out to be quite tough. For the first six months I looked OK, but then there was an injury in the second-half of the season and I couldn't add to my account."
Yarmolenko was limited to playing in 18 out of Dortmund's 34 Bundesliga matches, finishing the season with six goals in 26 appearances in all competitions.
The 28-year-old joins free transfers Jack Wilshere and Ryan Fredericks, veteran goalkeeper Lukasz Fabianski and young promising centre-back Issa Diop on the Hammers summer arrivals list.