Manchester United had wanted the midfielder, who is preparing for the Olympic football final, but he opted to join PSG on a four-year contract as part of a massive spending spree.
The French club have already signed Zlatan Ibrahimovic and Thiago Silva and the €45million (£35.5m) acquisition of Moura takes the spending on that trio to more than £120m.
PSG said in a statement: “Paris Saint-Germain and Sao Paulo FC have reached today an agreement for the definitive transfer of Lucas Rodriguez Moura Da Silva.
“The player and Paris Saint-Germain have also signed an agreement from January 2013 to July 2017.
“The player will join Paris Saint-Germain and his new teammates in January 2013 for the second half of the season 2012/2013.
“By signing a young talent of the quality of Lucas Rodriguez Moura Da Silva, Paris Saint-Germain is already preparing the future.”