Senate President Stephen Parry will resign after the UK Home Office confirmed he is a British citizen.
Senator Parry revealed on Tuesday he may be a dual citizenship as his father was born in the UK. He confirmed this was the case on Wednesday.
Senator Parry said he would be submitting his resignation as Senate president and Senator for Tasmania to the Governor-General on Wednesday.
"With a heavy heart I inform you that I have received advice from the British Home Office that I am a British citizen by virtue of my father's birthplace, thereby being a dual citizen under the provisions of the Australian Constitution," Senator Parry said in a statement.
"Because my departure is rapid and an unexpected event, I will not have the usual opportunity to address you [my colleagues] in the Senate one last time.
"I wish to thank all of you as colleagues, many of whom I regard as good friends - from all quarters of the chamber - for your support and confidence in me."
In a statement, Attorney-General George Brandis thanked Senator Parry for his "long and distringuished service" to the Senate and Australians.
"Since his term of service commenced in 2005, Stephen has been an outstanding advocate for the interests of Tasmania and a significant contributor to the Parliament in a number of roles.
"He brought to the role of President authority, dignity and fairness – qualities acknowledged by all sides of politics."
Mr Brandis said the Senate was now expected to refer the matter to the Court of Disputed Returns under section 376 of the Commonwealth Electoral Act.
Senator Parry has served as President and Deputy President of the Senate for more than six years.
His father moved to Australia from the UK in 1951.
In his maiden speech, Senator Parry said he was 'Tasmanian by birth and [came] from a line of many generations of Tasmanians'.
"In fact, I am a descendant of the First Fleet convicts who arrived on 26 January 1788 onboard the ships the 'Scarborough' and the 'Prince of Wales'," he said in August 2005.
"I left home at the age of 16 - much to the joy of my mother, I think - joining the Tasmanian police force as one of their youngest ever recruits.
"After 10 years as a police officer, I became a funeral director, eventually buying the long-standing family business with my wife, Allison."
Tasmanian colleague Eric Abetz praised Senator Perry saying in a statement, he "has been a tremendous servant of the people of Tasmania since 2005 and there are many people, like myself, who are deeply disappointed by the news that he will be leaving the Senate."
Senator Parry is the eighth politician to be caught up in Australia's dual citizenship saga. Five others - including former deputy prime minister Barnaby Joyce - were declared ineligible to serve in parliament by the High Court last week.
A by-election will be held in Mr Joyce's former seat of New England on December 2.
- with AAP
