British Prime Minister Boris Johnson urged parliament to back his post-Brexit deal with the European Union and open a new relationship as a "friendly neighbour" with the bloc.
Britain and the European Union were signing the deal on Wednesday and the British parliament will approve its implementation, ending over four years of negotiation and safeguarding nearly a $1 trillion of annual trade.
Both sides said the occasion was a chance to begin a new chapter in a relationship forged as Europe rebuilt from World War Two, but which has often seen Britain as a reluctant participant in ever-tighter political and economic integration.
Johnson, in a specially convened sitting of parliament, said he hoped to instead work "hand in glove" with the bloc when its interests aligned, using Britain's new-found sovereignty to reshape the British economy.
"Brexit is not an end but a beginning," Johnson said. "The responsibility now rests with all of us to make the best use of the powers that we regain, the tools that we've taken back into our hands."
Parliament's lower house will vote on legislation that implements the deal at around 1430 GMT and, with both main parties due to vote in favour, it is expected to easily pass. The upper house of parliament then debates the bill and it should become law around midnight.
Earlier, against a backdrop of EU flags, top EU officials signed the treaties struck on December 24 to preserve Britain's tariff- and quota-free access to the bloc's 450 million consumers.
"It is of the utmost importance for the European Union and the United Kingdom to look forward, in view of opening a new chapter in their relations," the bloc said in a statement, calling for joint action on climate change and international affairs.
A British Royal Air Force plane was then due to take the documents to Johnson before returning to Brussels with a signed copy bearing the bloc's golden stars on the blue leather folder.
Britain formally left the EU nearly a year ago and the new partnership agreement will regulate ties from Jan. 1 on everything from trade to transport, energy links and fishing.
After both sides have signed, the deal will be in place until the end of February, pending final approval by the European Parliament to make it permanent.