The 24-year-old had been linked with a move to the Reebok Stadium for much of the winter transfer window following the sale of Gary Cahill to Chelsea.
Ream’s arrival is subject to international clearance, but he is expected to seal the deal, which will see the defender sign a three-and-a-half year deal with the Trotters.
And manager Owen Coyle was visibly pleased to have completed the signing, telling the club’s official website: "First and foremost we are absolutely delighted to secure Tim's services.
"He is a US international, a player that year-on-year has progressed and got better, and he will continue to do that.
"He was trailed by a number of clubs, including West Brom and also Arsenal,
who tried to sign him in the summer, so it is great that he sees his future here.
"Tim is everything that we want in the players we are bringing to the club when we spend in the transfer market.
"He is young, has a tremendous attitude and a winning mentality. I know he will fit in well with the rest of the squad here at Bolton."
