The Australian supermodel, who is married to Lord of the Rings actor Orlando Bloom, said that she is "proud" to represent an Australian airline because she is so patriotic.
Kerr told the Herald Sun: "I grew up with Qantas, which is such an iconic Australian brand. I'm proud of my Australian heritage and I'm so excited that I will now be able to represent Australia's premium airline around the world.
"I travel frequently and from the moment I step onboard a Qantas flight, I feel at home."
Qantas boss Alan Joyce said that he is very pleased with Kerr's signing, saying: "Miranda Kerr is one of the most photographed and recognisable people in the world."
Kerr has previously revealed that she and Bloom regularly have to travel between New Zealand - where he is currently filming The Hobbit movies - LA, the UK and Australia.
Previous Qantas ambassadors include Grease actor John Travolta, athlete Cathy Freeman, racing driver Mark Webber and golfer Greg Norman.
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