Liberal member for Bennelong John Alexander has announced his resignation from Parliament saying he mostly likely holds British citizenship.
He announced that he'll stand again for parliament in an upcoming by-election, after renouncing his UK citizenship.
Earlier this week, Mr Alexander, sought advice on whether he is a UK citizen through his father Gilbert Alexander who was born in England in 1907 and arrived in Australia in 1911.
Mr Alexander said he hadn't received official confirmation of his dual citizenship, but said the "balance, the probability of evidence is that I most likely am".
"The obligation that I have is that once I do not hold the view that I'm solely Australian I must resign. Having determined that late yesterday, to my satisfaction, just my choice, I felt I had to resign, that's why I have chosen to do," he told reporters in Sydney.
The former tennis star said he spoke to Prime Minister Malcolm Turnbull on Friday, and told him of his intentions.
"He encouraged me to be decisive, to act expeditiously, and to put things beyond any question of doubt and that's what I think the people of Bennelong want," he said.
He will be the second member of the House of Representatives forced to resign because of their dual citizenship.
Barnaby Joyce is facing a by-election in New England, after discovering he was a New Zealand citizen, because of his father's birth.