Donovan, who previously had a temporary spell with the Toffees in 2010, has regularly been linked with a return to Goodison Park and an agreement has now been reached for the 29-year-old to spend a further two months in England.
Everton manager David Moyes will first have Donovan back at his disposal for the Premier League fixture at home to Bolton Wanderers on 4 January. The American will remain with the Blues until after the Merseyside derby against rivals Liverpool on 25 February and could play up to 11 games, depending on their FA Cup progress.
Donovan told the Everton website: “The opportunity to return to Everton and play for such a well-respected club and a manager that I hold in such high regard was something that was simply too good to pass up.
“I thoroughly enjoyed my time at Everton in 2010 and I’m hopeful that we can experience similar success this time around. I want to thank David Moyes and Bruce Arena, as well as executives from both clubs and Major League Soccer, for allowing me this unique and special opportunity.”
The signing will provide a significant boost for Everton, who have struggled for consistent form in the Premier League this season after a summer during which Moyes made little investment in the transfer market and lost Mikel Arteta to Arsenal.
Moyes told Everton’s website: "I am delighted that we have managed to get Landon back. He will give us some good experience over January and February.
"He did well for us when he was over two years ago and hopefully will return with those same qualities. His season has just finished and like last time we need him to hit the ground running because the games come thick and fast at this time of year."