The 21-year-old arrived at Old Trafford along with his twin brother Fabio from Fluminense in 2008, and his performances for the first team have warranted a call-up to the Brazil squad.
Rafael expressed his delight at securing his future, telling the Premier League giants' official website: “I am so happy to sign a new contract.
"I love playing for Manchester United, there is a great team spirit here and a real desire to win.
"My time here has been unbelievable; winning two league titles, a league cup and a Club World Cup has made me hungry for more trophies.
"I would like to thank Sir Alex for his belief in me and I would also like to thank the fans for their support.”