Matthew Niall can once again call himself an Australian.
The 41-year-old father of three, living in Denmark, had his application to resume his Australian citizenship approved by the Department of Home Affairs on February 14.
Mr Niall told the ABC it was still sinking in.
"My first reaction was one of relief," he said.
"I'm so happy to have it back … because I've never not felt Australian.
"I'm very grateful to the minister, that they've actually stepped up and expedited this unbelievably quickly.
"But the other question remains about other people that are in this situation."
Last week, Mr Niall highlighted the plight of Australians who unknowingly and automatically lost their citizenship under an outdated law.
Under section 17 of the old citizenship act, Australians over the age of 18 who acquired a second citizenship automatically ceased to be Australian citizens.
That section of the law was repealed in April 2002, with the government of the day acknowledging it was outdated and saying up to 700 people a year were losing their Australian rights due to the law.
But Mr Niall, who got his Irish citizenship and passport in 2001 at the age of 19 while still living in Australia, had his Australian citizenship revoked and his passport cancelled last year.
The issue only came to light when he tried to get Australian citizenship by descent for his two young daughters, but did not come up when he successfully acquired Australian citizenship by descent for his son in 2008.
"Now we actually have an opportunity to plan the future," Mr Niall said.
"I want to be back home, and now we can actually work towards that."
Parents relieved but will continue advocacy for others
His mother, Roz Niall, said she was "absolutely ecstatic" that her son was considered Australian once again.
"We've got a nice bottle of champagne in the fridge, so I think we'll be opening that tonight," she said.
His father, Christopher Niall, said work remained to be done though.
"Tomorrow, we'll be coming back down to earth and focusing on the citizenship for the children," he said.
His parents said it was a major relief that their son could return to Australia at short notice if needed, without having to apply for a visa.
But while Mr Niall's citizenship has been resumed from February 14, it hasn't been reinstated.
"Which means for the last 21 years, he hasn't been Australian," Christopher Niall said, pointing out that Matthew's three children were born in that time.
"The legislation we believe is quite flawed in that regard."
He said the family would push to have the government alter the legislation to backdate the changes brought in with the repeal of section 17.
He added that many people had commented on a petition Mr Niall started, fearing they might be in the same predicament and wondering what to do.
"We know that other Australians would want to see the same thing. And if they're in that same situation as us, they wouldn't just do it for themselves, they would do it for their fellow Australians. I firmly believe that."
Mrs Niall said it would be easy to give up now that her son's citizenship had resumed, but it wouldn't fix the problem for other people.
"It would have been as simple as a question on a passport application or renewal … and Matthew wouldn't be 21 years and three children down the track," she said.
She also found it ridiculous that some ceased citizenships might never come to the notice of the department.
"Do we pick and choose who we strip of their citizenship?"
Case sparks widespread concern
North Sydney federal MP Kylea Tink, who advocated on the family's behalf and raised the issue in letters to government ministers, welcomed the move.
"I've spoken to the family and they're understandably over the moon. They never expected to find themselves in the situation they did, but are relieved to know Matthew's citizenship will resume," she said.
"Matthew's case has sparked widespread concern, a number of constituents have contacted us worried they are in the same situation.
"I'll continue to work with [Citizenship] Minister [Andrew] Giles and if those people do need help, we will support them too."
Mr Giles wrote in a previous letter to Ms Tink that the automatic loss of citizenship may never come to the notice of the Department of Home Affairs.
He and the Department of Home Affairs have been contacted for comment.
Mr Niall said he had heard from others who had also unknowingly lost their citizenship, and had also received letters from members of the public expressing support, confusion, disbelief and outrage.
"When I was going through it, I always felt alone in that I never met anyone else or heard from anyone else that had gone through the same thing," he said.
"I've just felt really isolated … even though I've had the support of my partner, my family and friends.
"It's strangely comforting in a way, that I'm not alone."
He said he wanted to close this chapter and move on, but added it was exciting to see people speaking publicly about the ordeal that he had been privately dealing with for more than 400 days.
He hoped it would provide a catalyst for action and that momentum was building for a change in legislation.
"The legislation doesn't fit with the morals and the values that Australians hold. And that needs to be remedied," he said.
"It's something that can't really be ignored.
"I'm so happy that this story is no longer going to be about me — it's going to be about this issue that we have. And now it's up to the politicians to find a solution to this."
