LONDON -- A timeline of key events related to Britain's decision to leave the European Union:
Jan. 23, 2013: British Prime Minister David Cameron promises a referendum on Britain's membership in the EU if the Conservative party is elected in the next general election. He does so to try to garner support among euro-skeptics within his own party.
May. 7, 2015: British voters elect a majority Conservative government. Cameron confirms in his victory speech that there will be an "in/out" referendum on European Union membership.
Feb. 20, 2016: Cameron announces that he has negotiated a deal with EU leaders which will give Britain "special status." He confirms that he will campaign for Britain to remain in the 28-nation bloc. The referendum date is set for June.
Feb. 21: Cameron is struck with a severe blow when one of his closest Conservative allies, the media-savvy Boris Johnson, joins the Leave campaign.
June 16: One week before the referendum, Labour Party lawmaker and "remain" campaigner Jo Cox is killed by extremist Thomas Mair who shouted "Britain First" before shooting and stabbing her.
June 23: Britain votes 52 percent to 48 percent to leave the European Union.
June 24: Cameron says he will resign in light of the results because Britain needs "fresh leadership" to take the country in a new direction.
July 13: Following a Conservative Party leadership contest, Home Secretary Theresa May becomes prime minister.
Oct. 2: May says that Britain will begin the formal process of leaving the EU by the end of March 2017. In order to do this the British government would have to invoke Article 50 of the EU's Lisbon Treaty.
March 29, 2017: The British government formally triggers Article 50, setting in motion a plan for Britain to leave the EU on March 29, 2019.
June 8: A general election called by May to bolster her party's numbers in Parliament to help with the Brexit negotiations backfires as her Conservative Party loses its majority and continues in a weakened state as a minority government.
July 7, 2018: May and her Cabinet endorse the so-called "Chequers Plan" worked out at a fractious session at the prime minister's country retreat. It leads to the resignations of Brexit Secretary David Davis, Foreign Secretary Boris Johnson and others who favor a more complete break with EU.
November 25: EU leaders approve a withdrawal deal reached with Britain after months of difficult negotiations. May urges British Parliament to do the same.
December 10: May delays the planned Brexit vote in Parliament one day before it is to be held because it faces certain defeat. She seeks further concessions from the EU.
December 12: Conservative lawmakers who back a clean break from the EU trigger a no-confidence vote in May over her handling of Brexit. She wins by 200 votes to 117, making her safe from another such challenge for a year.
January 15, 2019: The Brexit deal comes back to Parliament, where it is overwhelmingly defeated on a 432-202 vote. A no-confidence vote on May's government is scheduled for Wednesday.