Ayew has signed a deal until the end of the season after leaving Qatari club Al Sadd, where he scored 22 goals in 39 games and won the domestic double in a season and a half.
He will wear the shirt number 42 during his time on Trentside.
Ayew said: “It’s a great feeling to sign for Nottingham Forest.
“I know how big the club is and I know how much the club means to the city and the fanbase. It’s always been difficult whenever I’ve played against Forest and at The City Ground and I love the stadium.
“Steve Cooper is someone who knows me very well and knows how to work with me both on and off the pitch. We have a strong relationship, he’s a special coach and a special human being and someone who I really look up to.”
“I know what I can bring to the team, I’m ready to give my all and make sure that we are able to stay in the Premier League.”
The 33-year-old reunites with Steve Cooper having previously played under the Forest Head coach at Swansea City, scoring 35 goals in 84 appearances under the Welshman’s tutelage.