The talented 18-year-old joins the famous South American club from the Stars Of Africa Academy.
He will link up with the Fluminense Under-20 team.
The club are based in Rio de Janeiro, and the player has already linked up with his new teammates.
Madiba made a name for himself with his displays for South Africa at the Under-20 Africa Cup of Nations, where Amajita emerged as the competition winners.
He said on iDiski Times: "I am very grateful to Fluminense for the opportunity to do what I love most and become one of the few South Africans in history to play in Brazil.
"I believe I can contribute to the team, so the fans should expect the best from me. I am here to help the team with goals, win titles, and I hope to use Brazilian football to improve."
Orlando Pirates teenage defender Mbekezile Mbokazi has been left out of South Africa's final Under-20 squad for the upcoming FIFA U-20 World Cup in Chile, scheduled from September 27 to October 19.
Amajita coach Raymond Mdaka says Tylon Smith's transfer to Queens Park Rangers will motivate young players to follow in his footsteps.
Wolverhampton Wanderers have completed the signing of Colombia winger Jhon Arias from Fluminense.
Joao Pedro marked his first start for Chelsea with a stunning brace as the Blues defeated Fluminense 2–0 to book their place in the Club World Cup final.
