Nigel Hallett has become the second member of Parliament to quit the Western Australian Liberal Party in this term of Government, with the veteran backbencher defecting to the Shooters, Fishers and Farmers (SFF) Party.

Mr Hallett follows Rob Johnson in quitting the Liberal Party in the past few months and will become the SFF's second WA MP.

The Government will still have a majority in the Legislative Council, with 16 Liberal MPs and five Nationals in the 36-member chamber.

Mr Hallett was dumped earlier this year from the Liberal Party's ticket for the Upper House's South West region for the 2017 election, in a move that appeared to end his parliamentary career.

But Mr Hallett will now try to win re-election in the 2017 poll with the SFF.

Mr Hallett was relegated from the South West ticket in February, in favour of Manjimup shire president Wade de Campo and former shadow treasurer Steve Thomas.

Fellow Upper House MPs Brian Ellis and Liz Behjat were also bumped from winnable positions while former child protection minister Helen Morton was relegated to a spot on the East Metropolitan ticket which the Liberals are considered unlikely to win.

Mr Hallett has been an MP in the council since 2005, serving on the Barnett Government's backbench since the 2008 election.

He said he had decided he was better able to serve his constituents by leaving the Liberal Party and joining the SFF.

"I think farmers feel let down and are looking for a lot more out of their politicians," Mr Hallett said in a statement.

"I understand Australia is a trading nation and urgent changes are needed to boost research and development, biosecurity, technology and innovation."

Shooters, Fishers, Farmers party welcomes Hallett

Rick Mazza, who became the first SFF member to be elected to Parliament in 2013, said his party was very pleased to welcome Mr Hallett to its ranks.

"Nigel Hallett is very well respected by his constituents and brings over a decade of parliamentary experience to the Shooters, Fishers and Farmers here in Western Australia, we are delighted to accept his membership application," he said.

"Nigel's involvement in the future of the South West Region and the agricultural industry is one that he has passionately advocated for."

Premier Colin Barnett said he was disappointed by Mr Hallett's decision.

"I expect people elected as Liberal members would continue to serve as Liberal members," Mr Barnett said in a statement.

Mr Hallett's decision has also drawn an angry response from part of the Liberal Party ranks, with one preselector taking aim at the MP on social media.

"Nigel, you're an utter disgrace. You owe your entire political career to the Liberal Party. If you had a shred of dignity or self respect you would quit Parliament altogether," Brent Fleeton, a Bayswater councillor who was involved in the South West preselection process, posted on Facebook.

Labor leader Mark McGowan seized on the latest defection from the Liberal Party, saying it again showed there was disunity within the Government's ranks.

"There is clearly a lot of leadership division and turmoil within the Liberal Party," he said.

"The Government is more focused on itself than it is the people of Western Australia and the in-fighting going on is not good for the state of Western Australia."