A man waves a Union Jack and a European Union flag together on College Green outside the Houses of Parliament in June 2016 during an anti- Brexit protest. (Justin Tallis / AFP/Getty Images)

Visual timeline of key events related to Britain's decision to leave the European Union

Cameron promises a referendum on EU membership

British Prime Minister David Cameron delivers his long-awaited speech in London on the United Kingdom's relationship with the European Union. Cameron had promised a referendum on EU membership should the Conservatives win the next election.

(Oli Scarff / Getty Images)

Scottish voters decide in a referendum to remain part of the United Kingdom rather than become an independent country

Enumerators look into a ballot box in Aberdeen, Scotland, as it is emptied at the count center for the Scottish referendum on independence from the UK.

(Peter Macdiarmid / Getty Images)

British voters elect a majority Conservative government

A voter enters a polling station at the Old Post Office in the village of Brokenborough in Wiltshire, England. The vote for a new government was one of the most closely fought general elections in the UK's recent history. Cameron's Conservatives won.

(Matt Cardy / Getty Images)

Cameron says an EU deal will give Britain ‘special status’

Prime Minister David Cameron speaks to the news media following a cabinet meeting at Downing Street in London. Cameron returned to London after two days of talks in Brussels with EU leaders; he said a deal would give the United Kingdom "special status" and includes changes to EU treaties.

(Chris Ratcliffe / Getty Images)

Media-savvy Boris Johnson joins the Leave campaign

London Mayor Boris Johnson announces outside his London home that he will back the Leave EU campaign.

(Chris Ratcliffe / Getty Images)

One week before the referendum, Labor MP and Remain campaigner Jo Cox is killed

Flowers surround a picture of Jo Cox during a vigil in Parliament Square in London. Cox was a member of Parliament and rising Labor Party star who had campaigned for Britain to stay in the EU. She was killed in northern England by extremist Thomas Mair, who shouted "Britain First" before killing the mother of two.

(Dan Kitwood / Getty Images)

Britain votes 52% to 48% to leave the EU

Chelsea pensioners arrive to cast their votes in the EU referendum at Royal Hospital Chelsea in London. The United Kingdom went to the polls to decide whether or not the country wished to remain within the European Union.

(Dan Kitwood / Getty Images)

Cameron resigns, says Britain needs ‘fresh leadership’ to take the country in a new direction

British Prime Minister David Cameron resigns on the steps of 10 Downing Street in London. The unexpected victory of the "leave" campaign was a crippling defeat for the Conservative Party leader who campaigned vociferously to remain in the EU.

(Dan Kitwood / Getty Images)

Following a heated leadership contest, Home Secretary Theresa May becomes prime minister-elect

British Home Secretary Theresa May waves with her husband, Philip John May, outside the Houses of Parliament. Following a heated leadership contest, May became prime minister-elect when her competitors withdrew from the race.

(Christopher Furlong / Getty Images)

May says that Britain will begin the formal process of leaving the EU by the end of March 2017

British Prime Minister Theresa May delivers a speech about Brexit on the first day of the Conservative Party Conference in Birmingham, England.

(Carl Court / Getty Images)

The British Supreme Court rules that parliamentary approval is needed before Article 50 can be triggered by government

Satirical artist Kaya Mar poses with one of his paintings outside the Supreme Court in Parliament Square ahead of the ruling on whether Parliament has the power to begin the Brexit process.

(WPA Pool)

Britain's Parliament approves a bill giving the government the authority to invoke Article 50

A Remain supporter looks on during a demonstration in London. Britain's Parliament approved a bill giving the government the authority to invoke Article 50 of the EU treaty and launch two years of exit talks.

(Jack Taylor / Getty Images)

Scotland's first minister, Nicola Sturgeon, says she plans to have a second referendum on Scottish independence in late 2018 or early 2019

Pro-independence supporters pose with their faces painted with Scottish flag during a rally in Glasgow. Scots had voted overwhelmingly to stay in the EU.

(ANDY BUCHANAN / AFP/Getty Images)

May signs the letter that will trigger Brexit

British Prime Minister Theresa May, at 10 Downing Street, signs the official letter to European Council President Donald Tusk , invoking Article 50 and signaling the United Kingdom's intention to leave the EU.

(AFP/Getty Images)

Brexit formally triggered as letter is hand-delivered to EU council president

Britain's ambassador to the EU, Tim Barrow, left, shakes hands with European Council President Donald Tusk in Brussels after handing him the prime minister's formal notice of the UK's intention to leave the European Union under Article 50 of the Lisbon Treaty.