Former Queensland racing minister Steve Dickson has defected from the Liberal National Party to One Nation.
The member for Buderim announced he was jumping ship at a press conference with Pauline Hanson in his electorate on Friday morning.
Mr Dickson cited his wish for an amnesty for medical cannabis users as a key factor in his decision.
He said his appeals for action on the matter fell on deaf ears in the major political parties and Senator Hanson was the only one willing to take up the issue.
"A young lady who was in my office, just this Monday gone, has a brain tumour and was using this exact same product so that she can stay alive," he said.
"I called on the Premier of Queensland Annastacia Palaszczuk and also the Prime Minister of Australia Malcolm Turnbull over a week ago to grant amnesty, so that these people can access this life-saving drug to keep their children alive."
Senator Hanson has been advocating for medical cannabis to be legalised and this week appealed to Mr Turnbull to intervene and deliver an amnesty.
Mr Dickson, who was racing minister in the Newman government, emailed his former LNP colleagues to notify them of his defection on Friday morning.
He said both the LNP and Labor were out of touch with the electorate.
"The major parties have lost their way, now we have a chance to step up to the plate," he said.
Senator Hanson said there were no deals done to get Mr Dickson to join her party.
"I believe that it was just through sheer frustration that Steve felt that he was not being able to be a voice for the people of Queensland in his electorate," she said.
The Senator said Mr Dickson was concerned about much more than just an amnesty for medicinal cannabis users.
"He has spoken to me about so many other issues as well, that we need to see Queensland move forward," she said,
"It is stagnating ... there's no foresight or vision or leadership that's coming from (Premier) Annastacia Palaszczuk and neither does (Opposition Leader) Tim Nicholls have it."
Mr Dickson's defection means One Nation now has a representative on the Queensland's powerful crossbench, though Senator Hanson says he will not immediately be appointed as the party's state leader.
It also reduces the LNP's numbers to 41 in the state's hung parliament, putting it behind Labor's 42 seats.