Britain will take the first step on its "momentous journey" to a future outside the European Union when Theresa May launches divorce proceedings that will bring to an end a relationship of more than 40 years.
The Prime Minister has signed the letter that starts the formal exit process and the historic document will be hand-delivered by a senior diplomat to EU chiefs.
It will mark the start of complex and contentious negotiations that put the UK on course to break its ties with the Brussels club by the end of March 2019.
Mrs May will urge the country to "come together" as she looks to the heal the deep wounds caused by a referendum campaign that left the UK mired in division.
The PM's top team will gather around the Cabinet table at No 10 on Wednesday morning as she updates them on the content of the letter formally invoking Article 50.
Some time after 12.30pm, the premier will inform MPs that Brexit is being triggered and in Brussels, British ambassador to the EU Sir Tim Barrow will deliver the document to European Council president Donald Tusk.
Once it has been accepted, Article 50 has been officially launched.
The PM will tell the Commons she will represent "every person in the UK", including EU nationals, when she takes to the negotiating table.
"It is my fierce determination to get the right deal for every single person in this country," she will say.
"For, as we face the opportunities ahead of us on this momentous journey, our shared values, interests and ambitions can, and must, bring us together.
"We all want to see a Britain that is stronger than it is today.
"We all want a country that is fairer so that everyone has the chance to succeed.
"We all want a nation that is safe and secure for our children and grandchildren.
"We all want to live in a truly global Britain that gets out and builds relationships with old friends and new allies around the world.
"These are the ambitions of this Government's plan for Britain. Ambitions that unite us, so that we are no longer defined by the vote we cast, but by our determination to make a success of the result.
"We are one great union of people and nations with a proud history and a bright future. And, now that the decision has been made to leave the EU, it is time to come together."
Key EU figures agreed to enter into Brexit talks in a "positive spirit" during a series of telephone calls with Mrs May on Tuesday evening.
German Chancellor Angela Merkel, Mr Tusk and European Commission president Jean-Claude Juncker said the UK would remain a "close and committed ally".
Within 48 hours, the European Commission is expected to issue "draft negotiation guidelines", which will be sent to the 27 remaining states for consultation.
Their leaders will meet on April 29 at an extraordinary European Council summit to agree a mandate for chief negotiator Michel Barnier and clear the way for talks to begin in earnest in May.
The key point of contention as soon as Article 50 is triggered is the order in which different aspects of Brexit are approached.
Effectively, there are two issues to be settled - the terms of Britain's withdrawal from the EU and arrangements for future trade relations.
On top of that is a possible third negotiation on a "transitional arrangement" covering the period between the moment of departure and new trade rules taking effect.
Labour leader Jeremy Corbyn said: "The British people made the decision to leave the European Union and Labour respects that decision.
"Britain is going to change as a result. The question is how.
"The Conservatives want to use Brexit to turn our country into a low-wage tax haven.
"Labour is determined to ensure we can rebuild and transform Britain, so no one and no community is left behind.
"It will be a national failure of historic proportions if the Prime Minister comes back from Brussels without having secured protection for jobs and living standards.
"That's why Labour has set the clear priorities of full access to the European market, rights at work and environmental protection. And we will hold the Government to account every step of the way."
On Thursday, a white paper will be produced on the Great Repeal Bill, the legislation that will turn four decades of EU regulations into domestic laws.