It has come to this. Even a First Australian, descendant of the oldest living culture on Earth, has faced questions about whether he is eligible under the constitution to sit in the national parliament.

Patrick Dodson, known by many as the father of reconciliation, is renowned for his work as an Aboriginal advocate before entering Parliament as a Labor senator.

He says he is an Australian through and through, but public references to his father John "Snowy" Dodson having Irish heritage saw the senator fielding questions this week about whether he too could be a dual-national by descent.

Claims about Snowy Dodson's Irish background has raised questions about his son Patrick's eligibility to sit in Parliament. ( Supplied: Paddy's Road: Life Stories of Patrick Dodson )

Six politicians have already fallen foul of the dual-national constitutional crisis, including the former deputy prime minister Barnaby Joyce and former president of the Senate Stephen Parry.

Others have a cloud over their citizenship or the time taken to renounce an overseas link.

Senator Dodson — also a former Roman Catholic priest — has released a statement to the ABC outlining his Australian roots.

"I am an Australian. My father was an Australian. He was born in Launceston, Tasmania," Mr Dodson wrote.

The ABC has seen marriage, birth and inquest documents that list Snowy Dodson's birthplace as Launceston.

One document does list him as British, but that document is dated July 1947, a year before the concept of Australian citizenship was conceived.

So why was his heritage unclear?

There are references to Senator Dodson's Irish background online and in Parliament.

When former WA premier Colin Barnett spoke at a joint sitting of the state parliament to endorse him as an incoming senator last year, he spoke about the perceived link.

Sorry, this video has expired Colin Barnett tells WA Parliament about Pat Dodson's Irish-Australian father

"Patrick Lionel Djargun Dodson is a Yawuru man from Broome," Mr Barnett said.

"His father, Snowy, was an Irish Australian and his mother, Patricia, a Yawuru woman."

Senator Dodson has rejected this.

"The only known Irish connection in my family is my mother's mother's father," he wrote in the statement to ABC.

A biography of Senator Dodson written by his chief of staff Kevin Keeffe more than a decade ago had also raised uncertainty.

"Supposedly from Launceston, Tasmania, Snowy has left no track of his birth, family or schooling," Mr Keeffe wrote in the 2003 book Paddy's Road: Life Stories of Patrick Dodson.

He wrote the family had "no clues and no family connection has come forward".

"One old Aboriginal man told Patrick Dodson in later years that his father Snowy has been a stowaway on a plane that landed in Darwin, jumping out of a wheel-carriage before landing," he wrote.

"Another has suggested he was a draft-dodger who changed his name on leaving Tasmania.

"The family wondered if he might have been a Tasmanian Aboriginal."

In this political climate, questions of nationality are coming to some of the most unlikely parliamentarians.

That Senator Dodson has been forced to check his family history shows how farcical the citizenship saga has become.