Brecon and Radnorshire MP Chris Davies voted to support Theresa May in the no-confidence ballot of Conservative MPs.
Mr Davies was called into an individual 20-minute meeting with the Prime Minister before last night’s dramatic vote in Committee Room 14 of the House of Commons.
Mrs May survived the vote, winning the support of 200 of her party’s MPs against 117 who voted for her to lose her job.
The secret ballot was triggered by letters written to the party’s Chief Whip by 48 MPs angry at her Brexit policy, which they say betrays the 2016 referendum result.
Mr Davies, a keen Brexiteer, has publicly restated his support for the Prime Minister in a statement he released this morning.
Mr Davies said: "I met with the Prime Minister in a private meeting ahead of the vote. Earlier on in the day I made my feelings clear that I have grave concerns with parts of the proposed exit deal.
"The meeting lasted 20 minutes and I agreed to support the Prime Minister in this no confidence vote. There is no clear outright successor to the Prime Minister and with the UK on such a tight time schedule I do not want to give the opponents of Brexit in Parliament – of which there are many – the chance to delay and stop Brexit.
"The PM reassured me when I expressed my concerns and I will help work to get Britain out of the EU by the end of March next year."
Previously he had "reluctantly" backed Mrs May’s deal to leave the EU. That deal was not voted on by MPs on Tuesday, as had been planned, when it became clear that it would not win a Commons majority.
Yesterday, at a meeting of the influential 1922 Committee of Tory MPs, the Prime Minister made it clear that she would not remain the party’s leader at the next scheduled general election in 2022.
She begged for the chance to continue to negotiate a deal to leave the European Union, assuring sceptical MPs that she would seek to gain more assurances from EU leaders over the controversial Northern Ireland 'backstop’.