The 30-year-old, who left the Magpies upon the expiration of his contract this summer, has penned a permanent deal with the Championship side.
It is not the Killingworth-born schemer’s first experience of the City Ground, however, with Colback having spent two loan spells with Forest during the 2017/18 and 2018/19 seasons. During that time, he made 54 appearances and netted four times.
In his time at St. James’ Park, Colback – who received a call-up to the England squad during his first season on Tyneside – made a total of 102 appearances for United, scoring five goals.
The former Ipswich Town and Sunderland man, who swapped Wearside for Tyneside in 2014, joins Sabri Lamouchi’s men as they look to build on their seventh-placed finish in the second tier, having just missed out on the Championship play-offs this term.