The 19-year-old Wales international, who can play in either full-back position, will help ease a defensive crisis at the City Ground.
Forest have five defenders who are currently in the treatment room and Forest boss Billy Davies is delighted to be bringing in a player who can offer versatility.
"We are pleased we are bringing in an excellent player who can play a number of positions," Davies told Forest's official website.
"He is a first-class lad to have here and I am delighted to have him. Hopefully we will see the best of him."
Gunter joined Spurs from Cardiff in a £2million move in January 2008, but has struggled to break into the first team, making just 16 appearances for the White Hart Lane club.