The WA Liberals will preference One Nation ahead of the Nationals in some of the upper house seats at the forthcoming March state election.
The deal is in return for One Nation to preference the party above Labor in the lower house.
Premier Colin Barnett said the deal was a practical, pragmatic decision, and would benefit his government in winning a third term.
"What we're out to do is retain government and there's no doubt, in the Legislative Assembly, in the lower house, One Nation preferences will flow to the Liberal Party," he told reporters on Sunday.
"That will give us a buffer to some of our seats under challenge, so it's to our benefit to win government and beat the Labor party."
However, earlier in February Mr Barnett cautioned people against voting for One Nation, saying it would be hard to govern if the upper house was controlled by a minor party.
Recent polling showed One Nation would be the third most popular party with 13 per cent of the primary vote.
A new Greens poll found 33 per cent of Liberal voters would be less likely to vote for them if they made a deal with One Nation.
The Nationals WA leader Brendon Grylls said his party had sought a direct preference deal with the Liberals, and Mr Barnett had signified it would happen.
"While some political parties believe they own or influence preferences - we believe this shows great disrespect to voters," he said in a statement on Sunday.
"The people of Western Australia will always vote with their hearts and minds, and won't be told how to vote by a piece of paper resulting from a backroom deal."
Mr Grylls said the Nationals had strong support for their policies across the state, and that elections were not won on preferences, but on primary votes.
Federal Labor leader Bill Shorten labelled the deal as a desperate move by a party that had publicly denounced One Nation in the past, and ruled out Labor giving One Nation preferences.
"I think what's turning people off the mainstream parties is when the people of Australia think Turnbull or I are just interested in ripping each other down and not focusing on them," he said.
WA Labor leader Mark McGowan said he was disappointed with the Liberal party and labelled One Nation hypocrites.
"The Liberal party and One Nation have now done a desperate, sneaky, political deal to try and save Mr Barnett's hide," he said.
"One Nation has done a deal with the devil."
Mr McGowan said One Nation were siding with a party that supported the sale of Western Power and foreign jobs, opposite to their own political direction.
Mr Barnett admitted it would be a complex and unusual election.
"There are some unpredictable results to come," he said.
Share
