"Peter Garrett is trying to sell a book."
That's the response from Kevin Rudd in the wake of Mr Garrett's tough criticism of the former Labor prime minster.
"If Mr Garrett were serious about these accusations he would have made them five years ago. Not try to rewrite history now," a spokesman for Mr Rudd's office said on Monday.
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Rudd a 'megalomaniac': Garrett
In his biography Big Blue Sky, to be released on Wednesday, Mr Garrett accuses Mr Rudd of delivering a "trail of destruction and abandoned policy" and jeopardising the "safety" of Australia while in office.
He also believes supporting Mr Rudd, who first took the prime minister's post in 2007 before being ousted by Julia Gillard in 2010, was the worst mistake of his political career.
"I've been particularly strong in this book about leadership and Rudd's leadership and I think it needed to be said," Mr Garrett told Seven Network's Sunday Night program.
"Rudd wasn't someone who was easy to work with in that way, and his vanity and his exercise of power as prime minister was contrary ultimately, to me, to what good leadership is."
Mr Rudd returned as prime minister in 2013, after the party dumped Ms Gillard.
Labor lost government to Tony Abbott's coalition in September that year.
Mr Garrett was environment minister during Mr Rudd's first years as leaders.