The widely expected move was confirmed by the world football body's Executive Committee which met in German's financial centre Frankfurt ahead of the Confederations Cup final between Brazil and Argentina.
"The Executive Committee decided that the transfer of the Australian Football Federation into the Asian Confederation has been ratified," Blatter said.
"All parties involved are happy."
Australia normally win the Oceania qualifying group but under the current rules they have to play the fifth-placed team in the South American qualifying group for a place in the World Cup finals.
In 2001, they lost out to Uruguay over a two-match playoff.
(CRI June 30, 2005)