The 57-year-old's career has been very much up and down, but he now has the chance to establish himself as a top-flight manager.
Postecoglou's time at Celtic was extremely successful and he ended his stint at Parkhead by securing the domestic treble.
But things haven't always been that good...
Where is Postecoglou from?
The now Spurs boss was born in Athens, Greece, on August 27, 1965.
However, he was forced to move to Australia in 1970 when his father lost his business during a military coup.
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He emigrated to Melbourne with his parents when he was five and grew up there.
How did Postecoglou get into football?
The Australian national started out as a footballer when he was nine and joined local club South Melbourne.
Postecoglou was a left-back and remained with the club from 1978 to 1993, making 194 appearances and captaining the side.
His playing career came to an abrupt end due to a knee injury, but not before he played under Ferenc Puskas.
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His managerial career started at South Melbourne in 1996 and he won two league titles.
His next managerial role came within the Australian youth set-up but came to a shuddering halt after seven years.
Postecoglou engaged in a heated argument with TV pundit Craig Foster and was replaced in February 2007 after the Young Socceroos failed to qualify for the Under-20 World Cup.
After his on-air bust-up, he returned to Greece to manage in the third division and felt his managerial career at the top level was over.
But Brisbrane Roar gave him another chance in 2009 and he won back-to-back A League titles before moving to Melbourne Victory, and then got the Socceroos job.
Postecoglou signed a five-year deal with the national team in 2013 and they qualified for the 2014 World Cup.
Australia lost every match but turned in competitive displays against the Netherlands and Chile.
The Socceroos won the 2015 Asian Cup and qualified for the 2018 World Cup before Postecoglou resigned in 2017.
He moved to Japan later that year to take the job at Yokohama F. Marinos.
Postecoglou's first season was a struggle as the club just avoided relegation before winning the league in 2019.
Then Celtic came calling in 2021, and things have been incredible since then.
Rangers had just went through the 2020/21 league season unbeaten to claim the SPFL crown and looked miles ahead of their inner-city rivals.
But Postecoglou got Celtic playing beautiful football and they managed to win the league in his first year in Scotland.
He proved that was no fluke this season by retaining the league title and claiming both of Scotland's domestic cups to seal an incredible treble.
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Celtic were gutted to see the Australian leave but he now has the chance to rebuild Tottenham into a top side.
The road to Spurs hasn't been straightforward for Postecoglou, but he is ready for this next step.