Prime Minister Kevin Rudd has signed the instrument of ratification of the Kyoto Protocol.
Mr Rudd says it is the first official act of the new Government and demonstrates the commitment to tackling climate change.
The ratification document will be sent to the United Nations and it comes into effect 90 days after that.
Mr Rudd says Australia will be a full member of the Kyoto Protocol before March next year.
The agreement means Australia's greenhouse gas emissions should not be higher than 8 per cent above 1990 levels.
Ratifying the treaty was one of Labor's major campaign promises.
The Greens say the move makes today a historic day for Australia, but comes years too late.
Mr Rudd, Climate Change Minister Penny Wong, Environment Minister Peter Garrett and Treasurer Wayne Swan are now preparing to go to Bali next week for the United Nations conference on climate change.
Climate change... it's not a myth.
This evening Emily came around (she had left her work pass last Thursday), so she helped me cook a chicken and asparagus risotto for dinner.