It was a turbulent 10 years packed with political turmoil.
The public went to the polls in four general elections and a referendum that divided the nation and shaped the decade’s later years.
But it was the dozens of lives lost in the Manchester Arena bombing, the Grenfell Tower blaze and a series of violent attacks across the capital that saw the decade defined by terror and tragedy.
The shocking deaths of MP Jo Cox – shot and stabbed to death by neo-Nazi Thomas Mair in her constituency in 2016 – and Fusilier Lee Rigby – rammed with a car before being hacked to death in 2013 – horrified the nation.
Relatives and survivors are still searching for answers after the inquiry’s phase one report, published more than two years after the tragedy, found the London Fire Brigade’s preparation for a tower block blaze to be “gravely inadequate”.
In 2017, election campaigning was suspended for three days when 22 lives were claimed following an explosion at an Ariana Grande concert.
Dramatic changes to the UK’s political landscape began in 2010, when the Conservative Party gained power for the first time since 1997 in coalition with the Liberal Democrats.
David Cameron returned to Number 10 as the head of a majority government the following year, delivering a crushing blow to Labour’s Ed Miliband and Liberal Democrat Nick Clegg, who both went on to quit as party leaders.
The biggest political controversy of the decade was the UK voting to leave the EU after 52% of the public supported Brexit in 2016.
It was a victory for then Ukip leader Nigel Farage, who became one of the most recognisable political figures of the decade, and a humiliating defeat for Mr Cameron, who brought an abrupt end to his six-year premiership with a hasty resignation.
Mr Johnson promised to lead a “One Nation” government and urged people “to find closure and to let the healing begin” following a landslide Tory victory that saw the party win its biggest majority in Westminster since the 1980s under Margaret Thatcher.
After 18 months of campaigning – often bitter, frequently bizarre and sometimes barely believable – Donald Trump triumphed over Hillary Clinton and was elected President of the United States.
Spells of flooding destroyed homes while the “Beast from the East” froze the British isles in 2018, just a year before the UK recorded its hottest day on record.
WikiLeaks co-founder Julian Assange spent seven years of the decade seeking asylum in London’s Ecuadorean embassy to avoid extradition to Sweden on a rape allegation he had always denied.
Swedish authorities discontinued the rape investigation in November but, after being dramatically removed from the embassy building in April, Assange was jailed for 50 weeks in May for breaching his bail conditions.
Police linked the attack to another poisoning some months later, when Dawn Sturgess died in hospital after handling a contaminated perfume bottle.
Mark Duggan’s death at the hands of a Metropolitan Police marksman sparked nationwide riots and days of unrest in summer 2011, as buildings were set alight and protesters engaged in stand-offs with riot police.
Officers have been deployed in their masses for a series of protests across the decade, including at demos against student fee increases in 2010, anti-Brexit marches and, most recently, action staged by Extinction Rebellion.
The 2012 murders of schoolgirls April Jones, five, from Machynlleth in west Wales, and Tia Sharp, 12, from south-east London, prompted an outpouring of grief.
And police forces found themselves under pressure from a rise in knife crime, with scores of teenagers stabbed to death on the nation’s streets in recent years.
The actions of the press also came under scrutiny in Lord Justice Leveson’s inquiry into media standards. A series of revelations about phone hacking saw the closure of the News Of The World in 2011 and recommendations were made about the future of press regulation.
Despite some years filled with devastating lows, Britain gloried in a string of dramatic highs in 2012. The country became a sea of red, white and blue for the Queen’s Diamond Jubilee, ahead of the Olympic and Paralympic Games held in the capital later that year.
Interest in the royal family rose in 2011, when a then 28-year-old Prince William married Kate Middleton in a fairy-tale wedding held at Westminster Abbey.
All eyes were on a second royal wedding some seven years later, when Prince Harry married American actress Meghan Markle in a lavish and star-studded ceremony at Windsor Castle that was watched by millions on both sides of the Atlantic.
Some 888,246 hand-made ceramic flowers provided a scene of remembrance in November 2014 as the nation marked 100 years since the start of the First World War. There were also events for the 70th anniversary of D-Day, with elderly veterans making what was for many their last visit to Normandy to commemorate the events of June 6 1944.
Anders Breivik, disguised as a policeman, killed 77 people in two separate gun attacks in Norway in 2011.
Paris became a target for terrorism in 2015, when gunmen stormed the building of satirical magazine Charlie Hebdo and months later targeted the Bataclan concert hall.
In 2016, some 32 people were killed in terror attacks on Brussels and more than 80 were murdered in Nice when a lone terrorist drove a lorry into crowds celebrating Bastille Day.
Former entertainer Jimmy Savile was exposed as a serial child sex abuser in 2012, leading to the launch of Operation Yewtree, a criminal investigation into widespread sexual abuse.
Allegations against movie mogul Harvey Weinstein began to emerge in October 2017 – claims he has denied. The story developed as more women began to share their stories of harassment and assault in Hollywood and beyond.
The attack came just weeks after the UK’s terrorism threat level was downgraded to “substantial” from “severe”.
But with the nation divided over one of most contentious political issues of modern times, Mr Johnson’s top priority will be to keep his promise to end Brexit uncertainty by ensuring Britain starts the new decade by leaving the EU as soon as possible.