Prime Minister Boris Johnson has officially signed the EU Withdrawal Agreement paving the way for Brexit to happen next Friday.
He said it was “fantastic” and that the UK could now “move forward as one country” as he signed the deal hours after EU figures had done the same.
Johnson said this marked the end of “far too many years of argument and division” and pledged to build “a strong new relationship with the EU as friends and sovereign equals”.
He added that the government was focused on “delivering better public services, greater opportunity and unleashing the potential of every corner of our brilliant United Kingdom”.
The treaty was ratified in Brussels earlier on Friday by European Commission president Ursula Von Der Leyen and European Council head Charles Michel, before being taken to London.
Michel Barnier, who has been the chief Brexit negotiator for the bloc, watched on from behind the pair.
The Brexit deal gained royal assent from the Queen on Thursday and was passed into law.
Michel, former Belgium Prime Minister, said: “Things will inevitably change but our friendship will remain. We start a new chapter as partners and allies.”
He added: “Look forward to writing this new page together.”
The document will now be taken back to Brussels and a special copy will be given to the UK.
The European Parliament is expected to vote to approve the agreement on Wednesday.
Von Der Leyen and Michel took over their posts from Jean-Claude Juncker and Donald Tusk respectively at the end of last year.
There is still plenty of work to be done, however, with the UK setting an 11-month timeframe to thrash out a trade deal with the EU.