Aberconwy MP Guto Bebb has confirmed he will not be standing at the upcoming election.
Mr Bebb was stripped of the party whip when he voted against the government in a bid to stop a no-deal Brexit.
It comes as two former ministers - David Lidington and Amber Rudd - both announced their plans to step down. Mr Lidington, who was effectively Theresa May's deputy, announced his resignation just hours after his colleague Ms Rudd.
There was speculation Guto Bebb may stand in his constituency as an Independent.
There were also rumours the Brexit rebel was in talks to rejoin Plaid Cymru but he told ITV Wales Political Editor Adrian Masters that was not the case.
He retained Aberconwy in the 2017 general election with a small majority of just 635 votes.
He stood down as defence minister last year so he could be free to endorse a second referendum.
He has been vocal of his criticism of Prime Minister Boris Johnson, saying his leadership would be "disastrous" for the party.
He said he was still a member of the Conservative Party - although he said he doesn't think it will remain in place in the foreseeable future.
"The way in which this Prime Minister has been willing to erect customs barriers between different parts of the United Kingdom is quite frankly unacceptable. So I don't think I will be rejoining once my membership comes to an end", he said.
He told Adrian Masters he would spend time supporting colleagues of the Remain alliance during the election campaign.
"I am happy to support (Labour's) Stephen Doughty who been a fantastic voice in highlighting the damage Brexit will cause.
"I am not going to do anything to damage my friends in the Conservative Party... who I wish well in a personal level, but I will be supporting colleagues who have been working with me over the past 18 months who in my view deserve to return to this place."