The Honduras international has been granted a work permit to play in England and will join up with the Latics when his contract with Sporting Kansas City expires in January
The 26-year-old has US citizenship having moved there at the age of 12 but represents Honduras, the country of his birth, at international level.
And he is set to join his compatriot Maynor Figueroa at the DW Stadium upon the expiry of his contract, news which has delighted Latics boss Roberto Martinez.
He told reporters: "We prepared an excellent case for Roger and it is great news for us that he can now join up in January.
"He is a player we have been following closely since June 16 2010, when he made his debut in the World Cup versus Chile.
"In that game, he showed tremendous potential and slowly he has been developing into an exciting footballer over the last three seasons in the MLS and has enjoyed terrific experiences at international level, specifically his role with Honduras in the Olympic games.
"The games versus Spain and Brazil in that tournament showed the winning and strong mentality that he possesses which will be an important asset to our squad."
Espinoza also revealed his happiness at having sealed a move, saying: "This has been a dream for me to play in England and I am so grateful for the club who have worked so hard to make this happen.
"I just can't wait now to join up with Maynor and all the guys and get to work."