The 17-year-old Brazil youth international will not join until the next winter transfer window as he is not allowed to make the move until after his 18th birthday.
"The player has signed a pre-contract agreement and is expected to join us in January 2012 on a long-term deal," Chelsea said in a statement on their website.
Piazon is currently at the South American Under-17 Championships, having made his name at the Under-15 tournament in 2009 - played in England - when he finished as top scorer with 10 goals.
No fee was revealed for the player, but recent reports suggested the deal could be worth as much as ?£8million depending on numerous clauses being activated.
Source: PA
Source: PA