Joe Hockey says if he stayed in politics, he would have focused on getting even with the people who backstabbed him.
The former federal treasurer will start a new role in January as Australia's ambassador to the United States.
He says he still has "three or four years of desire" to contribute to the country.
"It's just that politics at the end of the day beat me," Mr Hockey told Sydney businessman Mark Bouris in an online interview.
"If I was going to stay, it would be overwhelmingly about getting even with people that brought me down."
Labor deputy leader Tanya Plibersek said it was an extraordinary admission.
"The former adversaries he is talking about are the prime minister and the foreign minister - the very people he'll be having to report to as ambassador to Washington," she said.
Former senior Australian diplomat Ric Smith said there was a long record of political appointees to Washington going back to the 1940s.
Mr Smith said Americans were interested to know "can this person pick up the phone to the prime minister, the foreign minister, the defence minster and sort out a problem with them?"
Prime minister Malcolm Turnbull said Mr Hockey was a "great Australian".
"He is a passionate patriot but has a good understanding of how Washington works already," he said.
Mr Hockey was elected to parliament in 1996 after a career as a lawyer working in banking and finance.
He retired from parliament in September, after Mr Turnbull ousted Tony Abbott, and his seat of North Sydney was retained by the Liberals at a by-election on the weekend.
Foreign Minister Julie Bishop thanked outgoing ambassador Kim Beazley for his significant contribution to advancing Australia's interests in the US since 2010.
Mr Beazley starts a new role with the Australian Institute of International Affairs in January.
Assistant treasurer Kelly O'Dwyer said she hadn't heard Mr Hockey's remarks directly, but added: "It doesn't sound to me like the sort of comment that Joe would make".
She told ABC's Radio National she believed he was one of the great Australians and would do the nation proud as ambassador.
