The couple became the company's artistic directors in 2008 on a three-year contract, but Contactmusic reports that they will now stay on until 2013.
The company's owner Ian Darling praised the pair's work, claiming that they have "transformed the company and the way many people feel about it".
He added: "I'm pleased they will stay to build on what they have already achieved in terms of quality and diversity of productions, artform development and education."
Meanwhile, Blanchett and Upton said: "It is a really great privilege to lead Sydney Theatre Company. We hope more and more people, especially those in Sydney, will find their way to the company and join us on this incredible ride."