The ABC has called 40 seats out of the 59 in the state's lower house for Labor, with five for the Liberals and four for the Nationals, with 10 undecided.
While the 17 per cent swing away from Labor would usually be celebrated by a cock-a-hoop opposition, most of those votes went to independents and minor parties.
Labor's margin at the 2021 election under former WA premier Mark McGowan was a record victory in Australia.
Prime Minister Anthony Albanese congratulated the Labor premier on his "resounding victory".
"This is an extraordinary result from someone who has transitioned to premier after Mark McGowan chose to step aside and has shown extraordinary leadership on behalf of West Australians," he told reporters in Canberra on Sunday.
"The result was outstanding. There was always going to be a drop from the quite frankly stratospheric result of the 2021 election."
WA Labor holding the state is a boost to the federal party after the Liberal National Party won Queensland in their state election last October.
The federal election will almost certainly be held in May, after the threat posed by ex-Cyclone Alfred derailed plans for an announcement to be made this weekend.
Mr Albanese had been expected to call the election for April 12, which would have allowed Labor to avoid handing down a budget later this month that is expected to show a return to deficit.
Cabinet Minister Murray Watt said WA Labor had shown it was a "formidable government and formidable campaign machine".
"What we saw last night in WA is clear proof that Western Australians trust Labor when it comes to supporting them with their cost of living," he told ABC's Insiders.
"It's obviously a very strong endorsement for Premier Cook and WA Labor, and we certainly take heart from that."
Asked about swings in the outer suburbs in areas that include federal seats, Senator Watt said a "correction" was to be expected.
But there were a couple of extra electorates, including Moore and Bullwinkel which Labor will be "chasing", he said.
"We'll be fighting very hard to maximise the number of seats we can achieve in WA, as we will across the country," Senator Watt said.
Nationals Leader David Littleproud said the WA premier had been able to distance himself from federal Labor on key issues including live sheep exports and on environmental protections.
"There are lessons for everybody, you can't ignore that," he told Nine's Today.
"What that shows is that there was a mood for some swing in Western Australia.
"How that translates federally, I think comes back to that primary question, do you feel better off after three years of Anthony Albanese?"
Nationals Senator Bridget McKenzie said Mr Cook was a "very popular premier who chose to lock the prime minister out".
There had been "promising swings" in Labor-held seats in the outer suburbs including Hasluck, that the coalition could pick up, she told Sky News.
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