In his first 12 months at Number 10, the PM was tasked with navigating Brexit and the global crisis caused by Coronavirus.
Watch ITV News Political Correspondent Libby Wiener's analysis of Boris Johnson's first year as PM:
On the anniversary of the day he took over from Theresa May, the PM released a video reflecting on his first year in office and asked the public to be "absolutely clear" that coronavirus had presented his government with the biggest challenge "since the Second World War".
But he promised to press on with his domestic agenda and believes after a tough first year he will oversee a "successful" government going forward.
Here's a look at the issues that lie ahead for the Prime Minister as he enters a challenging second year in office - and a look back at the timeline of his 12 months in power.
Mr Johnson is keen to reopen as much of the economy as possible and has held out the prospect of life being back to normal by Christmas.
Even if the virus does remain under control, the economic damage caused by lockdown may take years to repair.
The current arrangements end on December 31 either with a deal to protect trade or without an agreement risking costs to businesses and holidaymakers.
Michael Barnier said the EU and UK have until “October at the latest” to strike a deal or risk the imposition of quotas and tariffs.
He said: “If we do not reach an agreement on our future partnership there will be far more friction."
Tensions have intensified after Foreign Secretary Dominic Raab announced the government will with Hong Kong in response to "grave concerns" over alleged human rights abuses associated with China's new security laws.
The challenge of how to cope with the increasingly assertive Asian superpower will be a major factor in the foreign policy agenda of Mr Johnson for years to come.
But a year on, and exacerbated by the coronavirus pandemic, there is little sign of a plan for the care sector.
Successive prime ministers have failed to come up with a solution of how to pay for the care required by an ageing population.
Number 10 said the government had sought views from across Parliament but the issue was complex and it would take time to develop a solution to the problem.
The Committee on Climate Change has warned the UK is not making the progress it needs to drive down emissions and prepare for the impacts of rising temperatures.
Here are some of the key events in Boris Johnson's first year as Prime Minister:
July 23, 2019
Boris Johnson is elected as leader of the Conservative Party after a campaign promising to take Britain out of the EU by the deadline of October 31 “do or die”.
July 24, 2019
August 20, 2019
August 28, 2019
September 4, 2019
Mr Johnson purges – including former chancellors Ken Clarke and Philip Hammond – who combined with opposition parties to pass the so-called Benn Act requiring him to seek a Brexit delay if he cannot get Parliament to back a deal by October 19.
September 24, 2019
October 17, 2019
October 19, 2019
Mr Johnson calls the first Saturday sitting of the Commons in 37 years in an attempt to get MPs to back his deal only to see them vote for an amendment requiring him to seek an extension to January 31 under the Benn Act. Mr Johnson dispatches a senior diplomat to deliver an asking for the delay.
October 29, 2019
Mr Johnson finally gets the general election he wants at the fourth attempt as Labour drops its opposition and a bill is passed allowing polling to take place on December 12.
The first case of a new coronavirus is identified in the city of Wuhan in the province of Hubei, China.
December 13, 2019
Mr Johnson secures an election victory with an 80-seat majority.
January 9, 2020
January 28, 2020
Mr Johnson defies pressure from the US and Tory backbenchers to announce that the Chinese tech giant Huawei can continue to play a limited role in providing the UK’s 5G network.
January 30, 2020
January 31, 2020
Earlier in the day two members of the same family test positive for coronavirus in the first cases to be diagnosed in the UK.
February 10, 2020
The Government declares coronavirus a “serious and imminent threat to public health” and takes powers to forcibly quarantine people as the number of cases in the UK reaches eight.
February 13, 2020
February 29, 2020
Eleven days after his divorce to his second wife is finalised, Mr Johnson and his partner Carrie Symonds announce they are engaged and expecting a baby.
The top civil servant at the Home Office Sir Philip Rutnam resigns, accusing Home Secretary Priti Patel of bullying.
March 3, 2020
Mr Johnson chairs his first meeting of the Government’s Cobra contingencies committee on Covid-19 – having left five earlier meetings to Health Secretary Matt Hancock – prompting accusations he was “missing in action”.
March 5, 2020
UK cases reach 90, as the first UK patient – a woman in her 70s – dies in the Royal Berkshire Hospital, Reading. A second person, a man in his 80s, dies the following day.
March 8, 2020
Mr Johnson is heckled during a visit to Bewdley in Worcestershire to meet residents hit by floods following criticism he had remained holed up in the Foreign Secretary’s Chevening estate while much of the country battled severe flooding.
March 11, 2020
The Covid-19 outbreak is declared a pandemic by the WHO.
March 16, 2020
Mr Johnson urges people people to avoid pubs, clubs and theatres, stop all non-essential contact and to work from home if they can after scientists at Imperial College warn 250,000 people could die unless stricter measures are adopted.
March 20, 2020
The Prime Minister orders pubs, restaurants, cinemas and gyms to close in a “huge national effort” to defeat the disease as Chancellor Rishi Sunak announces an unprecedented furlough scheme to protect jobs.
March 23, 2020
Mr Johnson puts the UK in lockdown with the closure of all non-essential shops and limiting when people can leave their homes, with fines for those who fail to comply.
March 27, 2020
Mr Johnson and Mr Hancock test positive for Covid-19, while chief medical officer Chris Whitty says he has symptoms of the disease and is self-isolating. The following day confirmed UK deaths from the disease pass 1,000.
April 2, 2020
The Prime Minister comes out of self-isolation for a brief appearance at the door of No 11 Downing Street to join the weekly mass clap for key workers.
April 5, 2020
Mr Johnson is admitted to St Thomas’ Hospital for tests as a “precautionary step” as his coronavirus symptoms persisted.
April 6, 2020
Mr Johnson is moved to intensive care after his condition worsened. Downing St says Foreign Secretary Dominic Raab will deputise for him as the number of people who had died in hospital after testing positive for coronavirus in the UK rises beyond 5,000.
April 9, 2020
The Prime Minister is moved back onto the ward at St Thomas’.
April 12, 2020
Mr Johnson is discharged from hospital to continue his recovery at Chequers, thanking NHS staff for saving his life. The hospital death toll of people who had tested positive for coronavirus in the UK passes the 10,000 mark.
April 29, 2020
Mr Johnson’s fiancee Carrie Symonds gives birth to her first child, a boy called Wilfred.
April 30, 2020
At his first press conference since being hospitalised, Mr Johnson says the country is “past the peak of this disease” and promises to deliver a “comprehensive plan” to ease lockdown.
May 5, 2020
The UK’s declared death toll from coronavirus rises to more than 32,000, passing Italy’s total and becoming the highest in Europe.
May 10, 2020
The Prime Minister sets out “the first sketch of a road map” for easing the coronavirus lockdown in a televised address to the nation, ending the “stay home” order and encouraging people to return to their jobs.
May 22, 2020
Media reports that Dominic Cummings, Mr Johnson’s top adviser, travelled to his parents’ property in Durham with his wife and child at the height of the pandemic in apparent breach of lockdown rules.
May 24, 2020
Mr Johnson says Mr Cummings “acted responsibly, legally and with integrity”, and “any parent would frankly understand what he did”.
May 25, 2020
Mr Cummings defends his actions at an impromptu press conference in the No 10 rose garden, saying he behaved “reasonably” and does not regret his actions.
He says that he went to Durham because of childcare concerns if he became incapacitated by the virus had that a trip to a local beauty spot was to test his eyesight after recovering from the disease.
The Prime Minister says shops across England will be able to open in June if they can meet the coronavirus guidelines to protect shoppers and workers.
June 23, 2020
In the biggest easing of lockdown regulations in England to date, the Prime Minister announces pubs, restaurants and hairdressers can re-open from July 4 as the two-metre social-distancing rule is relaxed.
June 28, 2020
Downing Street announces the Cabinet Secretary and National Security Adviser Sir Mark Sedwill is to stand down.
His national security brief is to go to Mr Johnson’s Brexit negotiator David Frost, a political adviser, amid accusations he lacks the necessary experience and that the job is being politicised.
July 14, 2020
In a major u-turn, Mr Johnson rules Huawei can no longer supply the UK’s 5G’s network and that existing kit must be stripped out after intelligence chiefs warn new US sanctions mean its products are no longer secure.