Former WA Liberal MP Ian Blayney has officially joined the Nationals, following a party meeting in Perth.
The Geraldton MP quit the Liberal Party in late July after losing his agriculture portfolio in a shadow ministry reshuffle under new Opposition Leader Liza Harvey.
Mr Blayney's defection boosts the number of Lower House Nationals to six, while the Liberals hold just 13 of the 59 seats in the chamber.
Mr Blayney, who sat as an independent for the past three weeks, said his decision to jump ship had nothing to do with the loss of his portfolio.
"I don't think you'd go through this entire process for a reason like that," he said.
"The 2017 election was very hard, and I didn't want to go through a similar election again, and so I just felt that I would be more effective and I'd probably have more support … if I went into that campaign as a member of the National Party."
Nationals leader Mia Davies said she was pleased to welcome Mr Blayney.
She denied the move would inflame tensions between her party members and their Government partners, the Liberals.
"I've spoken to Liza [Harvey] since the announcement was made that Ian made the decision to seek membership for the Nationals," she said.
"We're all focused on getting on with the job … and [we will] continue to have a professional working relationship going forward."
Mr Blayney's defection to the Nationals was not assured, with some MPs reported to have been concerned about it stoking tensions with the Liberals 18 months away from the next election.
Mr Blayney narrowly won his seat at the last election, surviving a swing of more than 20 per cent against him.
Tensions were high between the National and Liberal parties in the lead-up to the last election.
At that time, Mr Blayney launched a stinging attack on what is now his new party when Nationals member for the Agricultural region, Paul Brown, said he was quitting the Upper House and running for the Lower House seat of Geraldton because the Nationals needed to "protect regional WA from city-centric thinking".
