LONDON: A timeline of key events related to Britain's decision to leave the European Union:
January 23, 2013: British Prime Minister David Cameron promises a referendum on Britain's membership in the EU if the Conservative Party wins the next general election. He does so to try to garner support among euroskeptics 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.
February 20, 2016: Cameron announces that he has negotiated a deal with EU leaders that gives 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.
February 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 per cent to 48 per cent 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.
March 29, 2017: The British government formally triggers Article 50 of the EU's Lisbon Treaty, setting in motion a two-year process for Britain to leave the bloc on March 29, 2019.
June 8: A general election called by May to bolster her party's representation in Parliament to help with the Brexit negotiations backfires. 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. The plan leads to the resignations of Brexit Secretary David Davis, Foreign Secretary Boris Johnson and others who favor a more definitive break with EU.
November 25: EU leaders approve a withdrawal deal reached with Britain after months of difficult negotiations. May urges the British Parliament to back the agreement.
December 10: May delays the planned Brexit vote in Parliament one day before it is set 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. The House of Commons will end up rejecting May's agreement three times.
March 21: EU agrees to extended the Brexit deadline, just over a week before Britain's scheduled departure on March 29.
April 11: Britain and the EU agree for a second time to extend the withdrawal deadline to keep Brexit from happening without a deal in place. The new deadline is October 31.
June 7: May steps down as Conservative Party leader over the stalled Brexit agreement.
July 23: Boris Johnson elected new Conservative Party leader July 24: Johnson takes office as prime minister, insisting the UK to leave the EU on October 31, with or without a deal.
August 28: Johnson says he will temporarily shut down Parliament until mid-October, giving opponents less time to thwart a no-deal Brexit.
September 5: Johnson asserts he would rather be "dead in a ditch" than ask for another Brexit extension.
September 9: A parliamentary measure that prevents the UK from leaving the EU without a deal becomes law.
September 24: UK Supreme Court rules government's suspension of Parliament was unlawful.
October 10: Johnson and Irish leader Leo Varadkar meet and announce "pathway to a possible deal?"
October 17: UK and EU announce they've struck a deal after the UK makes concessions over Northern Ireland.
October 22: Johnson puts Brexit legislation on pause
October 28: Johnson asks the EU to delay Brexit again. The new deadline is January 31.
October 29: Parliament votes for a national election at the request of Johnson', who hopes it will break the Brexit stalemate.
December 12: Johnson wins a large majority in the general election, giving him the power to push through Brexit legislation.
January 23, 2020: EU Withdrawal Bill becomes law.
January 29: European Parliament approves the Brexit divorce deal.
January 31: UK officially leaves the EU at 11 pm, entering an 11-month transition period put in place for the two sides to negotiate a deal on their future relations.
December 9: Johnson and von der Leyen hold a dinner meeting in Brussels to see whether the differences can be bridged. They don't make a breakthrough but announce negotiations will continue for four more days, setting a December 13 deadline for a final deal or no-deal decision.
December 13: Von der Leyen and Johnson say negotiations will continue, vowing to go the "extra mile" to get a deal.
December 24: The UK and EU announce they have struck a deal, just over a week before the year-end deadline, that will allow tariff- and quota-free trade to continue.
December 30: EU leaders in Brussels and Johnson in London officially sign the agreement. Britain's House of Commons votes its approval with a day to go until the split becomes official on New Year's Eve.