In a statement,Mr Colvin said he had told the secretary of the Department of Prime Minister and Cabinet of his intention to leave the force before the federal election in May.
"This has been by far the hardest decision of my 30 years as a police officer,but I believe this is the right decision for me,for my family,and for the AFP,"he said.
A former high-ranking national security official said Mr Colvin had seen"the writing on the wall".
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"In the first month of this year he knew that he was not going to be extended irrespective of who won the election,for various reasons,” the former official said.
"Senior people in both parties had a view that they wanted a change,they wanted someone different in there,someone who is probably a little bit more favourable to their disposition one way or the other."
He said when it came to a replacement,“the game of thrones has well and truly already commenced”.