Western Australia's remaining Senate seats have been decided, with Pauline Hanson's One Nation Party and the Greens picking up the final two positions.

Key points: 10 of WA's 12 senators re-elected

10 of WA's 12 senators re-elected Labor, One Nation gain seats at expense of Liberals, PUP

Labor, One Nation gain seats at expense of Liberals, PUP Eligibility of One Nation's Rod Culleton in doubt

The results, which come more than four weeks after the federal election was held, show One Nation candidate Rod Culleton and incumbent senator Rachel Siewert from the Greens have been elected to the house.

Overall, the Liberal Party won five of the 12 Senate seats in WA, with Labor taking four, the Greens two and One Nation one.

The landscape remains largely unchanged, with 10 of the state's 12 senators having been re-elected.

The Liberals returned one fewer member with David Johnston failing to get back in, while Palmer United Party's Dio Wang also lost his position.

Mr Culleton and Labor's Louise Pratt, a senator from 2008 until 2014, are the new additions.

However, the eligibility of Mr Culleton remains in doubt due to a criminal conviction in New South Wales over the theft of a tow truck key during an altercation with its driver.

He is also awaiting trial in WA over allegations he stole a $27,000 hire car last year.

Mr Culleton has said he was convicted over the NSW charge in his absence because he was on bail for the WA charge.

The most likely outcome if his position is challenged and he is deemed ineligible is the seat will go to the number two or three candidates on the One Nation ticket — his brother-in-law Peter Georgiou or his wife Ioanna Culleton.

Mr Culleton struggled to defend or explain some of the party's key policies last week in his first sit-down interview since the election.

If he does enter the Senate, he will join a colourful crossbench, with One Nation and Nick Xenophon Team sending new members from Queensland and South Australia respectively.

New senators will attend "Senate School" in Canberra next month.

Greens 'not going backwards': Siewert

Ms Siewert, elected alongside fellow WA Greens member Scott Ludlum, said the Greens knew it was going to be a big job to return two senators in a double dissolution election.

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"It was a bit tighter than we thought ... there was a lot of small parties running, [a] very big ballot paper," she said.

She said the tight vote did not indicate the party was losing support, saying its House of Representatives vote had increased by more than 2 per cent and people were choosing to use their Senate vote differently.

"We're not going backwards ... [but] we need to look at how we make sure we're campaigning as strongly in the Senate as we've been campaigning in the House of Representatives."

Asked whether the Greens were prepared to work with the Government, Ms Siewert said there were "very serious issues" to be addressed, highlighting welfare changes and the royal commission into juvenile justice in the NT.