The former Swansea and West Ham player, turned down Nottingham Forest’s Premier League rivals Everton before the January transfer window closed.
Ayew becomes the club’s 29th signing since their return to the Premier League.
“It’s a great feeling to sign for Nottingham Forest,” said Ayew.
“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.
“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.”
He joined Al Sadd in July 2021 and scored 15 goals in 21 league matches as they were crowned Qatar Stars League champions last season, and overall scored 22 times in 39 games during his stay at the club.
Andre Ayew has earned 113 international caps for Ghana and has played at the last three World Cups.
He has scored 24 goals for the Senior National team.