Earlier this week it was revealed that Salop were close to confirming a deal for the 22-year-old central midfielder, who has made three first team appearances for the Championship club this season.
The former Brighton youth player, who enjoyed a successful loan spell at Plymouth Argyle last season, has been on the radar of Salop boss Steve Cotterill for a number of months.
And Cotterill has revealed that the club couldn't strike a deal in the summer to bring Fornah to the Montgomery Waters Meadow - but he's now delighted to be able to strike a deal at the second time of asking.
He said: "We're very happy to have Ty, he's a player we had our eye on last summer when Chris Hughton was in charge of Forest but that one couldn't materialise at the time. We revisited it in this window because we do need another midfielder in there so we're pleased to have Tyrese in the building. He's a very good lad, nice lad, and I'm sure he'll fit in.
"It's a position we've been light in so far this season but to be fair to the boys who are already there, we've been quite strong in midfielder so far and Tyrese will add that little bit more in there should we fall short through suspensions or injuries.
"He'll bring his defensive qualities more than anything else. He sits and passes it, and that allows us to make some movements in the squad and we're really happy to have him."
The midfielder began his career with the Seagulls before moving to Forest's U23s set up in 2018. He spent 18 months at the club before signing a loan deal with Porteugese side Casa Pia AC in early 2020 - however that spell was cut short due to the outbreak of the Covid-19 pandemic.
His next loan spell proved to be more productive - as he racked up 44 appearances during the 2020/2021 season at Plymouth.
On returning to Forest, Fornah penned a new deal with the club until 2024 - and so far this season he has played every minute for the club in the EFL Cup.