Mark McGowan standing down as WA premier in shock ...

WA Premier Mark McGowan has announced he is retiring from politics in a bombshell announcement.

Key points:Mark McGowan has announced he is quitting politicsHe became leader of the WA Labor party in 2012The premier said the job has left him "exhausted"

In a press conference held with just 45 minutes' notice, Mr McGowan said he would step down as premier and Member for Rockingham at the end of the week.

"The truth is I'm tired, extremely tired. In fact, I'm exhausted," he said.

WA Labor, under Mr McGowan’s leadership, swept to power in 2017, winning a landslide over a Liberal Party led by long-time premier Colin Barnett.

The 55-year-old was re-elected for a second term in 2021 in an extraordinary landslide, winning 53 of the 59 seats in the state's lower house.

The next WA election is not due until March 2025.

WA Premier Mark McGowan announced he was quitting politics in a snap press conference in Perth. (ABC News: Keane Bourke)

Deputy Premier Roger Cook and Health Minister Amber-Jade Sanderson are considered likely front runners to succeed to Mr McGowan.

"It has been an honour and privilege to serve the people of the state in my community over this time," Mr McGowan said.

"It is way beyond what I could ever have imagined my career would amount to."

'Relentless' pressure of the job

Surrounded by his cabinet at the press conference, Mr McGowan said the "relentless" pressures of political life had worn him down.

"I've loved the challenge of solving problems, making decisions, getting outcomes, and helping people," he said.

"It comes with huge responsibility that is all consuming each and every day. And, combined with the COVID years, it's taken it out of me."

"I'm not naturally confrontational. But, everyday I have to engage in argument and debate, and confrontation one way or another. And I'm kind of tired of it.

"That's political life. If you don't want to do that, don't come into politics."

Mr McGowan said he still believed in the Labor party, and had confidence it would win the next state election.

Sarah McGowan (centre) was at her husband's side as he announced his resignation.(ABC News: Keane Bourke)

'I'm convinced WA Labor can win, and will win … but I just don't have the energy or drive that's required to continue in the role as premier," he said.

A 'political juggernaut'

Mr McGowan said he would officially step down by the end of the week.

"It's now up to my colleagues to select my replacement," he said.

"I'm going to have a break for a while. I don't know what else I'll do.

Mark McGowan says leading the state through the pandemic took a toll on him. (ABC News: James Carmody)

"Once I'm rested and recuperated, I'll look for something to do."

ABC elections analyst Antony Green said few could have predicted the dominant place "mild-mannered" Mr McGowan would occupy in WA politics after his election defeat in 2013. 

"Having met him in 2013, I don't think anybody who met him when he had his first election as opposition leader [thought] a decade later he would be so dominant across Western Australia," Mr Green said.

"He turned out to be a juggernaut, politically."

The 'rock star' premier

Mr McGowan enjoyed overwhelming popularity in his second term throughout the COVID-19 pandemic, enacting the nation's strictest border policies.

The approach came with its critics, with some arguing it was a heavy-handed approach, and prompting then-Deputy Prime Minister Barnaby Joyce to describe WA as a "kind of hermit kingdom".

Criticism was even harsher when Mr McGowan postponed his initial border opening date.

However, he consistently argued his approach helped keep West Australians safe and bolstered WA's economy while the rest of the country struggled.

Mark McGowan with then-health minister Roger Cook enjoy a beer in July 2020, during the early months of the pandemic. (ABC News: James Carmody)

He said the stress of the political battleground throughout the pandemic played a significant role in his decision to resign.

"The COVID experience, basically three years … having to deal with all that, and all the pressure that was associated with that, that drained me a lot," he said.

Western Australia has enjoyed huge budget surpluses throughout Mr McGowan's second term off the back of iron ore royalties and GST payments.

The state is set to record a $4.2 billion surplus this year – a figure that rivals the federal surplus but falls short of the even bigger purses of $5.7 billion and $5.6 billion recorded in the years before.