ACT Labor senator Katy Gallagher was still a dual citizen of the United Kingdom when she nominated for the last federal election.
Senator Gallagher had taken the steps required to give up the UK citizenship she acquired through her father before nominations closed.
But she did not receive the letter from the UK Home Office confirming her renunciation until August 16 last year, which was two months after nominations closed.
The Prime Minister has said that Labor figures like Senator Gallagher who did not renounce other citizenship before the election should be referred to the High Court to decide their eligibility.
Senator Gallagher said she took all necessary steps to renounce British citizenship, including paying the processing fee.
She said she has legal advice, including from an expert on British nationality law which said she had taken all necessary steps.
Senator Gallagher said on Facebook she did not believe she should refer herself to the High Court, but conceded it would ultimately be a matter for the Senate to determine.
Her mother was born in Ecuador in 1943 to British parents, but Senator Gallagher said she was not and had never been an Ecuadorian citizen.
Cameron could be eligible to become Lithuanian
Labor senator Doug Cameron has revealed in his citizenship forms that he was potentially eligible for Lithuanian citizenship.
Senator Cameron was born in Scotland and renounced his British citizenship before nominating for Parliament.
His form shows his maternal grandparents left Lithuania for Scotland before his mother was born in 1915.
Last year, Lithuania changed its laws to allow for dual citizenship for descendants of Lithuanian citizens who left the nation before 1940.
But Senator Cameron said to acquire Lithuanian citizenship he would have to apply and he confirmed he had not done so.
Liberal Democrat Senator David Leyonhjelm's form shows all his parents and grandparents were born in Australia.
But in the section that asks for other relevant information, he wrote "I once asked my mother if my father was truly my father, but she was offended so I didn't ask again".
"I suspect immaculate conception," Senator Leyonhjelm wrote.