The Brazilian playmaker has praised the stature and ambition of his new club after finalising his transfer from Santos and ending months of speculation surrounding his future
The 22-year-old was linked with several top European sides, including Serie A giants AC Milan, but instead opted to continue plying his trade in his homeland.
"I am very happy. It is a huge joy, and a personal dream fulfilled to join Sao Paulo," the midfielder told the club's official website.
"I was in excellent mood once I heard of their interest. Now that everything has been finalised, I want to repay the faith of the club's board.
"What proved decisive in me agreeing to move were this great side's previous achievements, as well as the former icons who once played for this club."
Ganso will wear the number eight shirt and is expected to fill the void left by the departing Lucas Moura, who will join Paris Saint-Germain in January.