The 25-year old has made over 100 career appearences for Forest and has also been capped by the Republic of Ireland. He will be immediately be available to play, whilst also being available for the F.A. Cup but is cup-tied for the Johnstone's Paint Trophy, as he has already represented Forest this season.
Thompson is cover for Robbie Stockdale, who will be out for a month with a hamstring injury. He can play anywhere across the back-line and in central midfield.
John will wear the number 14 shirt vacated by Delroy Facey in the summer.