As MPs began resigning or were shown the door by the High Court, Mr Hollo began the process of investigating up to seven different entitlements to citizenship in December 2017 - a story that involves 14 months of legal wrangling, thousands of dollars and a 75-year-old Hungarian wedding certificate.

"I knew it was going to be complicated, I had no idea how difficult, how lengthy, how costly it was going to end up being," Mr Hollo said.

His mother was born stateless in a large Russian-Jewish community in Harbin, China, which did not recognise the foreigners as citizens. Mr Hollo's maternal grandparents were both born stateless - his grandmother in Germany, descended from Russian immigrants, and his grandfather also born in Harbin. His mother and her parents were expelled from China during the Cultural Revolution, finding their way to Australia as refugees.

Mr Hollo's father was born in Hungary, not long after the end of World War II. His grandparents fled Budapest in 1956, coming to Australia via a refugee camp in Austria.

On both sides, Mr Hollo's family history is punctuated by stories of fleeing regimes that were at best intolerant of Jews, and at worst committed to their genocide.

He was born in the United Kingdom to Australian parents, and had to get rid of his British citizenship - the easiest citizenship to cancel. It took just over six weeks to receive confirmation of renunciation.

Also relatively simple, was gaining confirmation from the German, Ukrainian and Russian embassies that he was not entitled to citizenship and had nothing to renounce. After many attempts Mr Hollo was able to ascertain in September he wasn't entitled to Chinese citizenship, leaving just his Hungarian citizenship as the last hurdle to a run at Capital Hill.

In February 2018, Mr Hollo was advised by a family friend that he was almost certainly a Hungarian citizen. What followed was months of conflicting legal advice, multiple submissions of paperwork and at least three points where he thought he was in the clear.

Just a week after Mr Hollo was publicly announced as the Greens' candidate for Canberra, he discussed the prospect of stepping down with party leader Richard di Natale's office as well as local leaders, as speculation grew about the possibility of a snap election during the Liberal leadership challenge in August.

As of January 29 this year, Mr Hollo was able to confirm he was solely an Australian citizen, receiving his certificate of Hungarian renunciation, signed by the Hungarian president and interior minister. The process could still be ongoing, if it wasn't for a letter from the Greens leader to the new Hungarian ambassador at the start of January, reiterating the urgency of the situation.

The final bill from the Hungarian lawyer isn't in yet, but the candidate believes he has spent thousands of dollars on the process, and counts at least three times when he thought the situation was sorted out, only to realise more steps were required.

It's a lot of work to do for a job that is in no way guaranteed. The Greens have a better chance of challenging Labor's Alicia Payne in Canberra than in other seats, but it is still a minor party. Mr Hollo worries many Australians would face similar battles to be eligible to run for parliament, and says many others wouldn't have the money or time to do what he has done.

"I'm far from unique, there will be many others who will be in the same situation and many who will say 'it's too difficult'. And our democracy is the weaker for that."

The only way to change the requirement for members of parliament to be Australian citizens and Australian citizens only, is by a referendum, as it requires constitutional change.

Mr Hollo believes there are higher priorities for constitutional reform than parliamentarian citizenship, but says there are other ways prospective MPs could be assisted to make sure they are eligible to run for parliament.

He wants the Department of Foreign Affairs and Trade to help those wanting to become MPs to renounce their citizenships, especially in cases where a person needs help understanding whether they have an entitlement to citizenship.

"It would be a pretty easy thing for the government to set up a unit within DFAT whose job it is to support Australian citizens seeking to renounce other citizenships so that they're eligible to run for parliament. Wouldn't be costly, wouldn't be difficult, could easily be done."

Mr Hollo contacted friends in the department, as well as contacts in the Department of Prime Minister and Cabinet and the Australian embassy, all of which came to nought at the time.

Constitutional expert Kim Rubenstein says the Katy Gallagher decision creates significant hurdles for those with citizenships that aren't simple to renounce.

"The reality is in a democratic framework with no certainty of when an election will be called, that people will basically have to start planning their nomination years before, to be certain they're able to renounce any other citizenships," said Professor Rubenstein from Australian National University's College of Law.

Professor Rubenstein said the interpretation in Gallagher's case, where the Court ruled "all reasonable steps" had not been taken because the UK required more documents, leaves Australia subject to the decisions and administrative practices of other countries being able to influence who can run for parliament here.