It has been reported that the 28-year-old defender held talks with Forest today, and that an agreement has been reached between the two parties.
Mills will join the Reds on a free transfer following his release from Championship outfit Bolton Wanderers.
According to The Nottingham Post, West Yorkshire club Leeds were interested in signing the centre-back, but it appears as if Forest have been able to convince the Englishman to move to the City Ground.
The fact that Mills is a free agent and will not cost any money in transfer fee is probably a major factor behind Leeds's interest.
Like Forest, the Whites need to be prudent with their money in the summer transfer window and cannot afford to spend loads.
However, the fact that Mills has not been deemed good enough to carry on at Bolton will be a concern for the Forest fans.