Harry Kewell is going to join the backroom team.
After just four months in charge of the National League side, Kewell was fired and has not worked since.
The coach decided against adding to his setup initially and was assisted by John Kennedy.
After winning the Scottish title and League Cup in his first season, Postecoglou has turned to a former player who will join as a first- team coach.
A key piece of advice from the 56-year-old was previously revealed by Kewell.
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He said that Ange told him to go his own way.
You run into trouble when you start listening to others.
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A year ago Celtic looked to the relatively unknown Ange Postecoglou to revitalise a club in turmoil and he silenced doubters by winning the Scottish Premiership title and League Cup.
After failing to win his first three matches at Parkhead, Postecoglou was knocked out of the European competition in the group stage.
The Australian insisted that he wouldn't change his philosophy of attacking, entertaining and relentless football and that he rebuilt a struggling side who were destroyed by Rangers the previous season.
The title win came at Tannadice on a Wednesday night in May, with the manager promising this was only the beginning for him.
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"I've had a lot of success but this is definitely the hardest challenge and the hardest year I've ever had," said the former Australian manager.
I didn't know what the strongest emotion was after the game.
I think there was a part of me that didn't want this to be the full stop.
The first foundation of a team that I hope will be successful in the future was built this season.
With Celtic's title win comes qualification for the group stages of the European football's premier club competition.
He told Sky Sports that he needed to be better next year.
The role of the players is to get there and make a difference.
It takes time to build a team that will continually make an impact.
We have had success in the transfer market without a lot of spending. We'll continue to grow in that area as we are the club we are.