Western Australia is facing a triple hit of state and federal by-elections, after Fremantle MP Josh Wilson announced his resignation in the wake of the High Court's latest ruling on dual citizenship.

The court decided today ALP senator Katy Gallagher was ineligible to sit in Parliament, leading to a wave of resignations from her along with Mr Wilson, Labor MPs Susan Lamb and Justine Keay and Centre Alliance MP Rebekha Sharkie — all of whom faced similar citizenship issues.

Those four by-elections could be held at the same time as a by-election in the federal seat of Perth, where Tim Hammond announced last week he was resigning due to family reasons.

Ex-Darling Range MP Barry Urban quit State Parliament after repeatedly lying about his past. ( Supplied: The West Australian )

A state by-election also needs to be held in the WA Parliament electorate of Darling Range, after disgraced former MP Barry Urban resigned over a damning parliamentary privileges committee report into his conduct.

Mr Wilson, who was elected in 2016, was drawn into the citizenship scandal after questions were raised over whether he renounced his UK citizenship prior to his nomination as a Labor candidate.

In documents provided to the citizenship register in December, it was confirmed he applied for renunciation of British citizenship on May 12, 2016, but it did not come into effect until June 29 — 20 days after the June 9 nomination deadline.

Wilson served as 'Australian citizen'

Following the High Court ruling, Mr Wilson stood in Federal Parliament to announce his resignation along with his intent to contest the by-election.

"I have not served a single day as the member for Fremantle and a member of this place as anything other than an Australian citizen," he said.

"Every opportunity I'm given to ask the people of Fremantle to trust me with that responsibility, of being their representative in the national Parliament, is an opportunity I relish.

"I was looking forward to doing it in the general election. I was looking forward to doing it as part of an election that would see the creation of the next Labor government, but I'm happy to do it in the next five or six weeks, and then again.

"I'm happy to be [judged] by the voters in my community on the basis of my principle and character and my work ethic and my record."

Mr Wilson and Centre Alliance member Rebekha Sharkie have both resigned. ( ABC News: Marco Catalano )

Fremantle 'safe bet' for Labor

Notre Dame University political analyst Martin Drum said Mr Wilson was a "pretty safe bet" to retain Fremantle.

He won the seat at the last election with a 2.12 per cent swing towards Labor and a 7.52 per cent margin, taking it out of marginal seat territory.

Dr Drum said it would be a surprise for the Liberals to contest the seat because they might regard it as unwinnable. It would more likely to be a by-election contest between Labor and the Greens.

The Greens won 17.74 per cent of the primary vote in Fremantle at the last election, up by 5.87 per cent.

Mr Wilson received 40.99 per cent of the primary vote, down by 0.36 per cent on the ALP's result at the previous election.

Dr Drum said the Greens would have to massively lift their performance to win Fremantle.

"The federal electorate is much bigger that the state electorate, and takes in a lot of Labor and Liberal voting areas that the state seat doesn't," he said.

"It would be a massive jump for them. They've never reached 20 per cent in the primary vote previously."

Tim Hammond quit as Perth MP to spend more time at home with his family. ( AAP: Rebecca Le May )

But Dr Drum said the seat of Perth, recently vacated by Mr Hammond, would be a much tighter race if the Liberals put up a candidate.

"The margin's smaller, and also demographic change means the Liberals perhaps are in with a chance of winning that seat," he said.