The 21-year-old, who was a transfer target for several Sky Bet Championship clubs this summer, has put pen to paper on a one-year deal with the option of another 12 months.
Laing was signed by the Black Cats from under the noses of his hometown club Newcastle in 2009. At the time, he was likened to then-England captain John Terry and was rated as one of the best prospects in the country.
Also able to play as a holding midfielder, Laing has represented England from Under-16 to Under-19 level, where he first came to the attention of Forest's former England youth coach Brian Eastick.
Laing made just one appearance in the Premier League for Sunderland in a 3-1 defeat against Wolves in 2011 and had a loan spell at Wycombe where he played 11 games in the 2011-12 season.
Despite his lack of experience, Manchester United took him on trial in April while Blackburn were also interested in the 6ft 3in centre-back and offered him a deal at Ewood Park.
Meanwhile, Forest's teenage goalkeeper Jordan Smith is on the radar of a handful of clubs in League One and League Two.