Australia's greatest ever goalscorer was a mainstay in Postecoglou's plans during 2018 FIFA World Cup qualification, scoring the double against Syria last month to ensure the Socceroos' progress to the final play-off against Honduras.
The veteran striker took to social media to show his appreciation for the coach.
“Want to say a massive thank you to Ange Postecoglou,” Cahill said.
“The last four years have been amazing and he has helped create memories that will last forever for our country.
“From the World Cup in Brazil, winning the Asian Cup and now to the biggest prize of qualifying for a fourth consecutive World Cup.
“His leadership and beliefs are infectious and I’m proud that I had the chance to share his journey with him and witness his love for our country.
“The most important part was the belief he instilled in us to play a style of football that could test any team we came up against. This for me sets Ange apart as someone that stayed strong to his values of changing the game in Australia.
“His saying that will stay with me forever is NEVER TAKE A BACKWARDS STEP. Want to wish Ange and his family all the very best in the future.”
Cahill arguably has the most to lose in terms of keeping his place in the Socceroos squad.
With the FFA set to name a replacement in the coming weeks, Cahill's dreams of playing in a fourth World Cup will now depend on whether Australia's new head coach values the 37-year-old's ability as much as his predecessor did.