Igor Jesus has signed a deal to 2029 with Forest and moves to the City Ground for a £10m fee,
"I'm really happy to be part of this new story, especially at a club like Nottingham Forest," said the 24-year-old.
"I didn't have to think twice about the offer, I embraced it. I embraced the project they sent me and I am delighted to be coming here and hope to do some great work."
Forest football chief Ross Wilson also said: “We have tracked Igor over a long period of time now and we are pleased he has now joined the Club. Igor joins a strong and united squad we are sure that he will settle in well to our group.
“The club continues to grow and develop all the time and we know Igor shares such ambition as he moves to Nottingham and the exciting challenge for him in the Premier League.”