Cahill wins Aussie fight
Cahill had been prevented from playing for the SocceRoos because he made a substitute appearance for Western Samoa Under-17s when aged 14.
The 23-year-old has been battling for nine years to play for the country of his birth and now football's world governing body has now agreed to change its eligibility rules.
Cahill was delighted at being given the go-ahead to play for Australia after a long hard battle.
"This is such a special moment," said Cahill. "Playing for Australia has always been the ultimate dream and now I can start thinking of playing in a World Cup."