SNP MP Lisa Cameron has announced that she has defected to the Conservatives.
The East Kilbride, Strathaven and Lesmahagow representative was facing a selection contest to remain as the SNP's candidate at the next general election.
She said she quit because of a "toxic and bullying" culture within the party's Westminster group.
Prime Minister Rishi Sunak and Scottish Tory leader Douglas Ross both welcomed her to the party.
Dr Cameron, a former NHS clinical psychologist, said she had received support from Mr Sunak after her mental wellbeing deteriorated in recent weeks, but had no contact from the SNP leadership.
She rowed back on her support for Scottish independence, describing it as divisive. She said she would instead focus on "constructive policies".
The MP claimed previously that she had been "ostracised" by the SNP after speaking out over the
handling of allegations against former Westminster chief whip Patrick Grady.
At the time, Dr Cameron did not rule out standing down and triggering a by-election if she did not win the SNP nomination.
The MP, who was challenged by party staffer Grant Costello, had been due to find out the results of the selection contest on Thursday.
SNP sources have told the BBC she was expected to lose.