International trade minister Greg Hands has resigned from the government to oppose the expansion of Heathrow.
A vote on whether to go ahead with plans to build a third runway at the airport is being put to the House of Commons on Monday.
Hands, MP for Chelsea and Fulham, is a longstanding opponent of the new runway.
It had been previously thought that ministers with constituencies directly affected by the expansion plans would be given dispensation to miss the vote.
Posting his decision on Twitter, Hands said: "As the Government will be whipping the vote Monday, this means I am resigning from the Government."
His resignation comes as the mayor of London, Sadiq Khan, vowed to join legal action against the third runway if it was approved by MPs.
Foreign secretary Boris Johnson is also opposed to the plans and once said he would lie down in front of bulldozers to stop it from going ahead.
Johnson is scheduled to be out of the UK on Monday so will not be at the vote.
