Aylesbury MP David Lidington voted with Theresa May, where her government suffered a historic loss.
Nobody in her current cabinet voted against her.
Her Brexit deal was voted down by 230 votes, the largest defeat for a sitting government in history.
The defeat is a massive blow for the current PM, who has spent two years hashing out a deal with the European Union.
Her plan was intended to set in stone Britain's departure from the EU on March 29, which would be followed by a 21-month transition period to negotiate a trade deal.
The debate saw some party members voting in non-traditional manner.
118 Conservative MPs - from both the Leave and Remain wings of her party - voted with the opposition parties against Mrs May's deal.
Three Labour MPs supported the prime minister's deal: Ian Austin (Dudley North), Kevin Barron (Rother Valley) and John Mann (Bassetlaw).
David Lidington office has been approached for comment.