passport is only a travel document, you only need it when you travel outside your country of residence.
I hope you know how to use it when you want to travel there from Thailand.
Mind you, you DO still need to have a Thai passport as well. Use the Thai passport to go in and out of Thailand.
Thailand: At the airport
Show Australian and Thai passports at the airline check-in desk.
Show Thai passport ONLY at the immigration check point on your way in and out.
Australia: At the airport
Show Australian passport ONLY on your way in and out.