Secretary of State for Wales, Sir Robert Buckland, has switched his support in the Conservative Party's leadership context from Rishi Sunak to Liz Truss.
Mr Buckland is the first Cabinet minister to publicly switch sides in the contest.
He had initially backed Rishi Sunak in the race to succeed Boris Johnson, citing his ability to lead the country through “challenging economic times”.
However, in an article for The Daily Telegraph, he said he now believed that Ms Truss’ economic proposals offered the best prospect of getting through the current crisis.
“Her plans give us our best shot at reaching our potential with the high-growth, high-productivity economy that we need not only to get us out of this crisis but to protect ourselves from the next,” he wrote.
Mr Buckland, the MP for South Swindon, became Secretary of State for Wales in a cabinet reshuffle after Simon Hart left the role in protest at Boris Johnson's leadership.
The new prime minister will likely perform their own cabinet reshuffle once they start their time in office.
It will come as another blow for Mr Sunak, the former chancellor, who has sought to stress his willingness to tell difficult truths while accusing his rival of peddling “fairytale” economics.
It will also reaffirm Ms Truss’s status as the clear frontrunner, with MPs hoping for a ministerial job in the new government looking to rally to the likely winner.
Earlier this week, former minister Chris Skidmore became the first MP to declare he was swapping his allegiance and backing Ms Truss.
In is article, Sir Robert said it was not easy changing sides mid-campaign but that he believed it was the right thing to do.
“As the campaign has moved on, and as I have listened carefully to both candidates, I have thought deeply about the issues that move me and what I want to see the next prime minister doing,” he said.
“Changing your mind on an issue like this is not an easy thing to do, but I have decided that Liz Truss is the right person to take our country forward.”