Everton seal deal for midfielder Gibson
The 24-year-old, a product of United's youth system, made 60 appearances for Sir Alex Ferguson's side since making his debut in 2005 but never nailed down a regular place in the side despite scoring a few spectacular goals.
Gibson has signed a four-and-a-half-year contract, Everton said on their website.
He is Everton's second new recruit since the opening of the January transfer window, following the loan signing of LA Galaxy's Landon Donovan.
Gibson, who has 17 Ireland caps and will be part of the squad for this year's Euro 2012 finals in Poland and Ukraine, could be in line for his debut against Aston Villa on Saturday.