EU flags at the National Assembly will be lowered at 23:00 GMT on Friday
Welsh politicians will mark the UK’s final day in the European Union later.
Flags will be lowered at the National Assembly in Cardiff Bay and Welsh Government buildings at 23:00 GMT – the moment the UK formally leaves.
In a speech in Cardiff First Minister Mark Drakeford will say Wales’ European identity will become more important after Brexit.
Conservative Welsh Secretary Simon Hart vowed the UK government would “make our union stronger”.
Mr Hart will take part in a cabinet meeting in Sunderland, the first city to back Leave as the referendum votes were counted in June 2016.
“This is not an end, but a beginning,” Prime Minister Boris Johnson is expected to say in a speech on Friday evening.
The National Assembly’s EU flags, which stand outside the Senedd and Ty Hywel buildings in Cardiff Bay, will be replaced with Welsh flags.
Wales voted to leave the EU at the 2016 referendum by 52.5% to 47.5%.
Mark Drakeford, who is Welsh Labour leader as well as first minister, will deliver a speech in Cardiff later on Wales’ future relationship with Europe.
“Today is a day for looking forward, not back,” he will say.
“We leave the European Union tonight. But Wales’ European identity continues. We will be a European nation so long as Wales exists.
“Wales remains a European nation and after 11pm tonight that identity becomes more important, not less.”
Mark Drakeford is seeking a close trading relationship with the EU
While the UK will leave the EU’s political systems on Friday night, it will enter a transition period where the country sticks to European Union rules.
This runs to the end of the year, during which time the UK government holds negotiations on a future trading relationship with the EU.
Mr Hart said: “Today marks a new chapter in our history as we finally deliver on the decision made by the Welsh people and leave the EU.
“We are leaving as one United Kingdom with a mission to build better infrastructure, make our streets safer, clean up our environment and make our union stronger.”
Andrew RT Davies was a prominent figure in the 2016 Welsh Vote Leave campaign, when he was serving as Welsh Conservative assembly group leader.
Mr Davies said: “It’s now incumbent on politicians of all colours to put the rancour and division of the past three years behind us and put our shoulder to the wheel to deliver a brighter future for Wales and the United Kingdom.”
Plaid Cymru had been among the parties battling for Remain. Earlier this week party leader Adam Price vowed to make Brexit work for Wales “as best we can”.
Mr Price said: “Wales will always be friends of Europe and nothing will change that.”
Vote Leave brought together Welsh politicians from the Conservatives and UKIP
Analysis by David Deans, BBC Wales political reporter
Wales’ vote to leave the European Union in 2016 amounted to a major turning point in the political history of the country.
It came despite support for Remain from Welsh Labour, which has dominated politics in Wales for a century.
Assumptions Wales was a pro-EU nation, in part because of billions in structural funds it has received, evaporated overnight.
It was a result that left senior politicians in Cardiff with a dilemma about how to respond.
Welsh ministers remain concerned at the impact that restrictions on trade could have on sectors of the Welsh economy reliant on EU markets, as well as who will control what replaces EU funds.
Labour lost six seats in Leave voting areas in Wales in December’s general election, to a Conservative Party promising to get Brexit done.
The question is, with assembly polls looming in 15 months, whether the Brexit debates of the last three years will have an even deeper impact on Wales’ political landscape.
