New Year's Day newspapers reflected the historic but still deeply divisive change, which will have repercussions for generations to come.
Under the terms of the prime minister's deal with the EU British people will no longer be free to live and work in Europe from Friday. "We have our freedom in our hands and it is up to us to make the most of it".
He initially campaigned against United Kingdom leaving the European Union but changed his mind after Britain voted to leave EU in 2016 vote. The UK voted to leave the European Union in 2016 and actually left on 31 January 2020, but leaders had until the end of 2020 to work out a trade deal.
"And yet it is also the essence of this treaty that it provides certainty for United Kingdom business and industry, because it means that we can continue to trade freely - with zero tariffs and zero quotas - with the European Union".
Customs border checks will be back for the first time in decades, and despite the free-trade deal, queues and disruption from additional paperwork are expected.
Most Labour MPs voted in favour after leader Sir Keir Starmer said a "thin deal was better than no deal".
Johnson added that "I am French".
"It's a divorce. you can't celebrate a divorce", he told RTL radio.
A government spokesman said: "The border systems and infrastructure we need are in place, and we are ready for the UK's new start".
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"And maybe we should have anxious most about COVID-19... not whether we have missing persons from a landslide ", she said.
Pro-Europeans lamented its failure to preserve seamless trade with Britain's biggest economic partner.
Public gatherings are banned due to the coronavirus outbreak, which has claimed more than 73,500 lives and infected almost 2.5 million people in Britain, including Johnson himself.
Billy Kelleher, a member of the European parliament for Ireland, which has the EU's only land border with Britain, linked Stanley's Johnson's decision to the UK's withdrawal from the continent-spanning Erasmus student exchange programme.
Later in the day, Boris Johnson signed a partnership agreement as British lawmakers approved the deal.
It is also eyeing another with India, where Johnson plans to make his first major trip as prime minister next month, and with incoming USA president Joe Biden's administration.
Other practical changes include how long Britons can visit their holiday homes on the continent, to travel with pets, and an end to British involvement in an European Union student program. It avoids the need for import taxes, or tariffs, which many businesses had feared.
The Road Haulage Association, an industry body, estimates that some 220 million new forms will now need to be filled in every year to allow trade to flow with European Union countries, including permits to even drive on the roads leading to ports like Dover.
The UK has reached several agreements with non-EU countries - such as Japan - to ensure continuity of trading arrangements for British companies from January 1.
The key financial services sector also faces an anxious wait to learn on what basis it can keep dealing with Europe, after being largely omitted from the trade deal along with services in general, which account for 80% of Britain's economy.
Rajneesh Narula, the John H. Dunning Chair of International Business Regulation at the Henley Business School, University of Reading, has warned that there could be hard months ahead as many large issues are left out of the current deal, which will add uncertainties to Britain-EU future relations.