The 30-year-old returns on a permanent contract following two successful loan spells in 2017/18 and 2018/19.
Colback made 16 appearances after signing on loan for Forest in January 2018, and returned on a season-long loan from Newcastle for the 2018/19 season when he made 38 appearances.
Having begun his career with Sunderland at the age of 10, signing a professional contract in 2008, the Newcastle-born player spent two seasons on loan with Ipswich Town before breaking into the first team in 2011.
Colback joined Newcastle on a free transfer in 2014 and consistently played for three seasons, helping them to promotion from the Championship in 2017, before falling out with manager Rafa Benitez. The arrival of Steve Bruce in 2019 offered new hope, but the midfielder didn’t play a game last season after being left out of the 25-man squad.
While not a like-for-like replacement, Colback will easily step into Ben Watson’s position should the out-of-contract player decide to return south where his family are based.
Meanwhile, the ongoing Matty Cash transfer saga remains far from resolved with the likes of Sheffield United and West Ham United among others believed to be interested in the 23-year-old right-back.