Labor didn't let its former national president Warren Mundine run for parliament for a reason, the party's deputy leader has declared.
But Tanya Plibersek says she will leave it up to the voters of the ultra-marginal electorate of Gilmore to discover what that reason was.
Mr Mundine will vie for the NSW seat for the Liberal Party at the next federal election.
"Warren Mundine has been very clear for the past 20 or 30 years that he wants a seat in parliament with any party that will have him," Ms Plibersek told ABC Radio National on Thursday.
"For a long time he was desperate for the Labor Party to give him a seat in parliament. There is a reason we didn't, and I'm sure the voters of Gilmore will discover that."
Nor was Labor leader Bill Shorten willing to be drawn on why his party back knocked back Mr Mundine's bid for parliament.
"It's a matter of record that Mr Mundine was unsuccessful in convincing the Labor Party, over many years, so he's going to try his hand in the alternative," he told the ABC news channel on Thursday.
Mr Mundine said he was a "Liberal for life" on Wednesday, the same day he joined the party and became its candidate for Gilmore.
He was a member of the Liberal Democrats - the minor party led by controversial libertarian David Leyonhjelm - until recently, but insists his third party will be his last.
A number of Liberal members quit or threatened to quit in disgust after his endorsement as candidate.
Prime Minister Scott Morrison says he intervened in the preselection and dumped locally-chosen candidate Grant Schultz because he had undermined sitting MP Ann Sudmalis.
But Ms Plibersek questioned why the prime minister couldn't have intervened earlier to save Ms Sudmalis, as he has done for other Liberals such as backbencher Craig Kelly.
Mr Mundine doesn't live in Gilmore, but the indigenous leader says it is his ancestral home.
He intends to rent before buying a farm in the electorate, with his son to work on the land.
"Win, loss or draw we are going to buy property down here," Mr Mundine said.
He also rebuffed concerns he may be ineligible to sit in federal parliament because one of his companies received government contracts, saying he would transfer his business interests to ensure there was no constitutional breach.
Australian Associated Press