It was announced in April that the Club had reached an agreement with Fluminense for the 18-year-old, who has now joined up with Pep Guardiola’s first team squad at the City Football Academy.
The Brazilian youth international has penned a five-year deal which keeps him at the Etihad Stadium until the summer of 2026.
He will continue to be involved in the senior set-up over the coming months, as part of the pool of young players whose development is aided by training regularly with Guardiola and his coaching staff.
Kayky said: “It's a dream to be here. I always followed Manchester City, as some Brazilian players are already here. I'm very happy."
A left-footed winger, Kayky joined Fluminense at Under-9 level and made his debut earlier this year at the age of 17.
Capable of playing off either flank, he went on to score three goals in 32 appearances for the Rio de Janeiro giants and became their youngest ever debutant and youngest goalscorer in the Copa Libertadores.
Everyone at Manchester City welcomes Kayky to the Club and wishes him all the best moving forward.