Margot James has resigned as culture minister to vote to stop Boris Johnson suspending parliament to force through no deal.
She has stood down as Minister for Digital and the Creative Industries after traipsing through the opposition voting lobby.
Ms James joined a Tory rebellion on an amendment to the Northern Ireland Bill prevents the next PM from proroguing Parliament to force the UK to leave the EU without a deal
The amendment passed by a majority of 41.
Some 17 Tories voted in favour of the amendment while a large number also abstained.
The number of rebels suggests Mr Johnson is in for a tough time when he takes over as PM.

He currently only has a working majority of three and this latest vote shows how difficult the Commons could be.
But the Prime Minister has decided not to sack any of those who disobeyed the whip instead suggesting it was an issue for her successor.
A Downing Street spokesman said: “The Prime Minister is obviously disappointed that a number of Ministers failed to vote in this afternoon’s division. No doubt her successor will take this into account when forming their government.”
Some abstainers may have had another reason such as prior commitments or illness.
The amendment is not an outright ban on suspending Parliament, but would make it much more difficult to do so.
Furious Northern Ireland minister John Penrose branded the amendment - to the unrelated Northern Ireland Bill - a "stitch-up".

Mr Penrose told MPs: "Not only is this amendment dangerously partisan, weaponising a Northern Ireland Bill for Brexit in a way which we usually, rightly, try to avoid.
"It could easily put us through all of that grief for no good reason at all if it fails to become law."
But Shadow Brexit Secretary Sir Keir Starmer said: "For Boris Johnson to try to shut down Parliament to force through a destructive ‘no deal’ Brexit would be a constitutional outrage.
"Now it would also be unlawful. A huge victory."
And Tory former Attorney General Dominic Grieve said MPs' role as "protectors of democracy" will be "shot to pieces" if they fail to stop propagation.
It comes hours after Boris Johnson said he would ramp up planning for No Deal after taking office.
The Tory leadership frontrunner has said he will take the UK out of the EU "do or die" on October 31, deal or no deal.
But today the government's official spending watchdog predicted No Deal Brexit would trigger a year-long UK recession starting this winter.
In the first forecast of its kind, the Office for Budget Responsibility said a recession would begin in the final three months of 2019 if the UK leaves without agreement.
The pound would drop in value instantly by 10% - while unemployment would rise by more than a quarter.
GDP would fall 2% by the end of 2020, around the same as the early 1990s recession and a third of what was seen in the 2008 financial crisis.
In all No Deal would add about £30billion a year to government borrowing from 2021, the OBR said - or, put another way, £577million a week.
That in turn would hike the UK's net debt by 12% of GDP by March 2024.
Despite the drastic findings, OBR forecasters said their stress test was "by no means a worst-case scenario".
17 Tory rebels who backed the amendment
Guto Bebb
Steve Brine
Alistair Burt
Jonathan Djanogly
Justine Greening
Dominic Grieve
Sam Gyimah
Richard Harrington
Margot James
Phillip Lee
Jeremy Lefroy
Oliver Letwin
Paul Masterton
Sarah Newton
Antoinette Sandbach
Keith Simpson
Edward Vaizey