Cheshire MP Antoinette Sandbach said rebelling against Boris Johnson was hard but "there are critical times when you have to do what is right".
The Eddisbury MP was one of 21 Tory MPs who voted against the government last nightin a move designed to rule out a no-deal Brexit.
It means another vote today that could force the prime minister to seek a delay to Brexit and the latest 31 October deadline.
Following the result, Ms Sandbach tweeted that the whip had been taken away from her, effectively expelling her from the parliamentary party.
She added she had rebelled "no matter what the personal consequences" and "most of my constituents would have supported a "soft" Brexit however they voted not a no deal".