Mancienne was a key player for Forest manager Stuart Pearce during his time in charge of the England Under-21 team and earned a call-up to the senior squad for the friendly against Germany in November 2008, although he did not play in Berlin.
The 26-year-old has put pen to paper on a three-year deal and becomes Pearce's fifth new arrival this summer following fellow defenders Louis Laing and Roger Riera and strikers Matt Fryatt and Lars Veldwijk to the City Ground.
Mancienne came through the youth ranks at Chelsea but played only a handful of games for the Blues. He got his first taste of regular first-team football at QPR but it was during another loan spell with Wolves where the defender came to prominence, making 46 Premier League appearances in two stints at Molineux.
In the summer of 2011 he left Chelsea for German club Hamburg and over the past three years has built a solid reputation for himself in the Bundesliga.
The signing of Manciennce, who is comfortable at both centre-half and at full-back and has played in a holding midfield role in the past, helps to ease Forest's injury crisis in defence with Jack Hobbs (ankle), Kelvin Wilson (calf), Eric Lichaj (groin) and Chris Cohen (knee) all set to miss the opening game of the Sky Bet Championship campaign at home to Blackpool on August 9.
Jamaal Lascelles also has a knee problem, thought to be tendonitis, which is hampering his pre-season preparations and is threatening his chances of being fit to face to Seasiders.