The Frenchman moves to The City Ground on loan from Premier League side Fulham.
Knockaert joins The Reds with a vast amount of experience under his belt, winning promotion from the Championship on three separate occasions, including last season with Fulham, and featuring regularly in the Premier League during his time at Brighton under Forest manager Chris Hughton.
Starting out his professional career at Guingamp, Knockaert helped them to promotion to the second tier in France before joining Leicester in 2012. After 100 games for Leicester and a Championship title to his name, he moved to Standard Liege in Belgium where he played, and scored, in the Europa League but after six months returned to England with Brighton.
The 28-year-old had great success with The Seagulls, scoring 15 times as they finished runners-up in the Championship in 2016-17, being named the Championship Player of the Year and selected for the PFA Championship Team of the Year.
He joined Fulham on loan last season, helping them to play-off success at Wembley, but now moves to The City Ground to team up with The Reds.