The Under-20 World Cup winner has penned a five-year extension with the club despite having been quoted as saying he would jump at the chance to join Roma
The Brazilian youngster had been strongly linked with a move to Italy, with Inter and Roma both understood to be monitoring his situation.
The 19-year-old midfielder revealed on Tuesday he 'dreamed' of wearing Roma's shirt, but he has now moved to commit his future to Sao Paulo.
"I have always made my respect for Sao Paulo clear. I am very happy with my renewal and even more motivated to stay on at the club and write my history here," the player told the club's website.
Casemiro, who won the Under-20 World Cup with Brazil, has made 43 appearances for Sao Paulo, netting seven goals.