Ex-Tory leadership contender Sam Gyimah said he felt "free" since defecting to the Liberal Democrats.
The East Surrey MP was one of 21 rebels barred from the Conservative Party for voting in favour of legislation designed to stop a no-deal Brexit, and shortly after, he joined Jo Swinson's party.
"There is no point being an outcast in your own party," he told talkRADIO's Mike Graham.
"Boris Johnson said 'do or die' he was going to deliver Brexit by October 31. He said this to win the Tory leadership contest. It was never deliverable, everybody knew that."
He continued: "I am free and liberated to be in a party where I can call these things out when I see them."
Mr Gyimah has always been vocal about backing a second EU referendum, and said Boris Johnson's calls for a December 12 election last night "proved him right".
"In the end, whether it's an election or a referendum we go for, we're going back to the people to resolve the deadlock," he added.
In the event of another referendum, the Liberal Democrat said he would back the option of Boris Johnson's deal against an option to remain, despite his party's staunch policy of stopping Brexit altogether.
"It has been clear for a long time that is the only way to resolve this impasse," he said.
"It is a fool who, when confronted with evidence, does not check with the people to say now we know what's negotiable, let us know if that's still what you want."