Postecoglou has been left in limbo for the last few weeks, as he awaited a decision on his future. Despite their triumph over Manchester United in the Europa League final, Spurs finished in 17th place in the Premier League, which has ultimately forced the club's hand.
"Following a review of performances and after significant reflection, the Club can announce that Ange Postecoglou has been relieved of his duties," Spurs said in an official statement.
"We are extremely grateful to Ange for his commitment and contribution during his two years at the Club. Ange will always be remembered as only the third manager in our history to deliver a European trophy, alongside legendary figures Bill Nicholson and Keith Burkinshaw.
"However, the Board has unanimously concluded that it is in the best interests of the Club for a change to take place. Following a positive start in the 2023/24 Premier League (PL) season, we recorded 78 points from the last 66 PL games.
"This culminated in our worst-ever PL finish last season. At times there were extenuating circumstances - injuries and then a decision to prioritise our European campaign. Whilst winning the Europa League this season ranks as one of the Club’s greatest moments, we cannot base our decision on emotions aligned to this triumph."
Postecoglou enjoyed a stellar start to his tenure at Spurs in the 2023/24 season, winning his first 10 games in charge and delivering some electrifying performances on the pitch.
However, the former soon tailed off and the north London side ultimately finished fifth in the Premier League.
That dip in form eventually carried over into the 2024/25 campaign, with Spurs recording their lowest-ever Premier League finish in 17th place, driven by a combination of horrendous injuries to key players and inconsistent performances.
Tottenham ended the season with just 38 points in the Premier League, their worst top-flight finish since the 1976/77 season.
They conceded 65 goals, went winless in eight of their last 10 league matches, and failed to beat a single top-six side after Christmas.
Postecoglou's Spurs also registered 22 losses in 38 games, which in any other season in English top-flight history with the same number of matches would have resulted in relegation.
"When I reflect on my time as Manager of Tottenham Hotspur, my overriding emotion is one of pride," Postecoglou said in a statement.
"The opportunity to lead one of England's historic football clubs and bring back the glory it deserves will live with me for a lifetime.
"Sharing that experience with all those who truly love this club and seeing the impact it had on them is something I will never forget.
"That night in Bilbao was the culmination of two years of hard work, dedication and unwavering belief in a dream.
"I sincerely want to thank those who are the lifeblood of the club, the supporters. I know there were some difficult times but I always felt that they wanted me to succeed and that gave me all the motivation I needed to push on.
"It's important to acknowledge the hard-working people at Spurs who gave me encouragement on a daily basis.
"And finally, I want to thank those who were with me every day for the last two years. A fantastic group of young men who are now legends of this football club and the brilliant coaches who never once doubted we could do something special."
Brentford's Thomas Frank is rumoured to be lined up to take over the manager's role at the club.