Everton have been locked in talks with Donovan's MLS club, LA Galaxy, and have now announced that a deal has been reached that will see the forward maintain his fitness during a break in the MLS calendar.
"It's all done now," said Moyes. "Landon will join us at the start of January. He will come in and add pace, he's a good finisher and is captain of the USA national team so he has that experience. He is the first of two or three players I want to bring in January."
Donovan's LA Galaxy team-mate, David Beckham, has already arranged a loan move to AC Milan as both players look to secure regualar football ahead of next summer's World Cup finals, where they could face each other when the U.S. and England face off on June 12.
It is the third time that Donovan has moved to Europe following largely unproductive spells with Bayer Leverkusen and Bayern Munich in Germany.
The 27-year-old was named as the MLS Most Valuable Player for 2009 and is the leading figure in his national side.