The back-to-back title-winning coach with the Roar has stood down, paving the way for a move to home-town club Melbourne Victory
Speculation had raged the 46-year-old was set for a move to home-town Melbourne Victory at the end of the season, and Postecoglou is now free to do so after stepping down on Tuesday. Assistant coach Rado Vidosic is expected to be named his replacement.
"I would like to express my gratitude to the owners, players and football staff of the Brisbane Roar," Postecoglou said via a statement on Tuesday.
"Their commitment and belief has created history for this club. I have been very proud to lead such an outstanding group of men, and I wish the club every success in the future."
Postecoglou joined the Roar in 2009, leading the club to ninth at the end of the 2009-10 campaign.
It was the following season when Postecoglou's side truly flourished, however, with the Roar going unbeaten throughout 29 matches and winning both the Premiers' Plate and the title.
Postecoglou guided Brisbane to back-to-back titles - the first club to do so in A-League history - with their 2-1 victory over the Perth Glory in Sunday's final.
But speculation had already arose about Postecoglou's future at the club, with the former Young Socceroos coach said to be a big-money target for Melbourne Victory.
Club director Chris Fong praised the influence of Postecoglou in his two-and-a-half season stint with Brisbane, crediting the coach for establishing the Roar as an A-League powerhouse.
"The Brisbane Roar would like to thank Ange for his commitment to the club over the last two and a half years, and the considerable role he has played in its success," Fong said.
"We respect how difficult this decision was for him and we wish him well in his new endeavours.
"Ange's departure marks the beginning of a new chapter in the story of the Brisbane Roar, and we are committed to ensuring we have the right people in place to continue the club's legacy with further successes."
The Roar's victorious squad released a joint statement soon after, wishing their former coach well: "As a playing group we would like to voice our appreciation for Ange Postecoglou," it read.
"He has been a huge part of many of us being at the club and helping to drive us to the success we have enjoyed over the past two seasons. We wish Ange every success in the next step of his career.
"While we appreciate all the effort he has put in, we are now focused on the next chapter in the club’s history.
"As a playing group we are committed to the club, it's ideals and philosophies and will continue to work hard in pursuit of future success."