The 23-year-old has been in Scotland for four years but will return home after agreeing a three-year deal. Paartalu had spells with Gretna and Stirling Albion before signing with Morton in 2008.
"I now have the opportunity to go back to Australia and be part of a successful team," the midfielder told the Greenock Telegraph.
"I would like to get my name known more in Australia and maybe get into a national team squad.
"That is a big incentive for me. I know the new coach [Ange Postecoglou] from my time with the under-17 Australian national squad. He is a well-respected coach in Australia,
"I am originally from Sydney and Brisbane is a 12-hour drive but I think it will work out very well. I have been over in Britain for four years now and it will be nice to go home and be closer to my family.
I have learned a lot about myself on and off the field in the last few years but I would like to go and test myself in Australia."
Roar had a poor season last year, finishing second bottom of the league, but Postecoglou has ambitious plans. "He wants to build a squad to challenge for the title," said Paartalu.
"That is possible because Adelaide finished first last season but ended up last this season. If a club can get a good squad together then they have a real chance of challenging for the league. A few of the boys at Road have got call-ups to the Socceroos squad. Hopefully it will be a good environment for me to push my career on."
"There have been a lot of ups and downs at Morton since I've been here. I have had some great highlights, like when I first arrived and helped them to stay up.
"I also scored a few long-range crackers that I'll always remember. I would liked to have played a bit more but there has been a lot of chopping and changing since I've been here. I am here until the end of the season and I will give my best until my contract expires."