Standing at an imposing 6ft 6, the 20-year-old arrives at the City Ground with an impressive resume, both at club and international level.
Cunha began his footballing journey with Santos, joining their academy at the age of 10.
After working his way through the youth ranks, he made his first-team debut at just 18, going on to make 24 appearances in Brazil's top flight.
In February 2025, Cunha made the switch to Botafogo, where he featured in the FIFA Club World Cup. He made headlines by scoring in the opening fixture against Seattle Sounders as Botafogo advanced to the Round of 16.
Cunha's development has also been recognised on the international stage. He played a key role in Brazil's triumphant campaign at the 2025 Under-20 South America Championship, earning eight caps and playing the full 90 minutes in each of those matches.
His defensive solidity helped Brazil keep three clean sheets en route to the title, and he missed just one game throughout the tournament.
"Jair is a young talent who has shown quality during his time in Brazil, and we are happy to have secured his signature," said Forest's Chief Football Officer, Ross Wilson.
"Jair has flourished in Brazil and now has new ambitions as he moves to the Premier League. We know he will be warmly welcomed into the group here in Nottingham."