The 31-year-old joins on loan for the rest of the season with the Club holding an option to make the move permanent if he performs well.
The Spaniard had fallen behind Ian Maatsen and Lucas Digne in Villa’s pecking order and has now joined a club where he can earn more minutes on the pitch and develop his talent.
Moreno joined Villa from La Liga side Real Betis in January 2023 and was Unai Emery's first signing when he joined the club.
Nottingham Forest chief football officer Ross Wilson is over the moon with the signing.
"Alex is a player we have had a long-standing interest in so we are naturally all very happy to see him arrive at Nottingham Forest.
"He has amassed significant experience in La Liga and the Premier League, and he brings all of that quality and experience to our group now."
This move comes after Forest defender Joe Worrall looks set to leave the club as Burnley are interested in grabbing his signature.