Western Australia's premier is set to overhaul the state's electoral system, months after assuring voters such a move was not on his agenda.

WA's six Legislative Council districts will be abolished and upper house MPs will instead be elected by the entire state, with regional votes no longer carrying greater weight than city votes.

The move has been slammed by the WA Nationals, who claim it will disenfranchise regional voters by reducing their representation.

"The premier lied to the people of Western Australia during the election campaign when he said electoral reform was not on the agenda ... he denied it again and again," Opposition Leader Mia Davies said on Wednesday.

WA will also scrap group voting tickets, which have been manipulated through so-called "preference harvesting" to get minor parties elected.

The Labor government will introduce legislation this week to enshrine the changes, which were endorsed by an expert committee led by former governor Malcolm McCusker.

Premier Mark McGowan tasked Mr McCusker with examining the system, in particular malapportionment in regional areas, soon after the election.

Each upper house region currently elects six representatives regardless of their populations.

Attorney-General John Quigley said votes cast by people in the Mining and Pastoral region at the last election were worth 6.22 times more than those cast in the metropolitan area.

Ending malapportionment could reshape the upper house given the Nationals' traditional dominance in regional areas.

Labor already holds 53 out of 59 lower house seats and an unprecedented upper house majority after a landslide election victory.

Mr Quigley insisted the reform would make WA's electoral system fairer.

"I do not accept that proposition at all that these laws are designed to favour Labor," he told reporters.

"The party that gets the larger percentage of the vote will get the larger percentage of the seats. That's what should happen in a democracy."

He insisted it would not come at the expense of regional representation.

"My message to regional voters is at this stage, 'Labor is the party of the regions'," Mr Quigley said.

"We have 21 members across the regions in Western Australia, more than any other party."

Under the changes, voters will elect 37 upper house MPs rather than the current 36.

WA will abolish group voting tickets, which allow parties to dictate the preference distribution when electors vote above the line.

Daylight Saving Party candidate Wilson Tucker was elected in the Mining and Pastoral region with 98 votes - a figure believed to be the lowest primary vote for a candidate elected to any Australian parliament.

His victory was made possible by preference deals which also catapulted Legalise Cannabis WA candidates to victories at the expense of the Greens.

Mr McGowan insisted changes hadn't been contemplated prior to Labor exceeding expectations by claiming an upper house majority.

"There's gaming and rorting of the system going on in Western Australia that needs to be fixed ... the whole system is broken," he said.

"It needs to be repaired and that's what these measures do."