Conor Purcell flew out of Bangkok on a Malaysian Airlines flight to Sydney via Kuala Lumpur late yesterday and he is due to arrive in Australia this morning.
The Irish-Australian was escorted to the airport by immigration officers.
He has been in immigration detention for two weeks after a court agreed to release him from prison.
He had been in jail since the anti-government Red Shirt protests were dispersed in May.
His release was negotiated in the court after he agreed to plead guilty to breaching Bangkok's state of emergency when he gave anti-government speeches on the Red Shirt rally stage.
A Bangkok surgeon who encouraged him to speak paid his fare.
http://www.abc.net.au/news/stories/2010/09/07/3005398.htm?section=justin