The Prime Minister will formally begin the Brexit process by triggering Article 50 on Wednesday.
Theresa May signed a letter which will begin the UK’s departure from the EU on Tuesday night.
At 12.30pm on Wednesday, the letter will be delivered to the European Council in Brussels by Britain’s ambassador to the EU, Sir Tim Barrow.
This will give official notice that Article 50 of the Lisbon Treaty has been triggered.
A two-year negotiation process will follow, expected to lead to the UK leaving the EU on March 29, 2019.
Theresa May will address the House of Commons at around the same time as European Council President Donald Tusk receives the letter.
She is expected to say: “It is my fierce determination to get the right deal for every single person in this country.
“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.”
The development comes after a majority of MSPs backed the First Minister’s plans to hold a second independence referendum by the spring of 2019.
The Scottish Conservatives, Scottish Labour and Scottish Liberal Democrat parties opposed the move at Holyrood.
The Scottish Government will attempt to secure a section 30 order, the legislative instrument which would allow the Scottish Parliament to hold the vote, from the UK Government.
However Theresa May’s government has said it will not grant the request, with the Prime Minister saying “now is not the time” for another referendum.
As well as signing the letter, the Prime Minister also spoke to EU leaders by phone on Tuesday night.
The European Commission is expected to issue negotiating guidelines within two days before formal discussions begin.
Ahead of the Prime Minister’s statement, Labour leader Jeremy Corbyn said that Britain was going to change.
He 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.”