MPs will today begin a two-day debate on the bill to trigger Article 50, giving the Prime Minister the go-ahead to launch formal negotiations for Britain to leave the European Union.
Discussions on the 'Brexit bill' will continue to midnight with a vote taking place on Wednesday evening.
What is the Brexit debate about?
The European Union (Notification on Withdrawal) Bill will allow Theresa May to trigger Article 50 of the Lisbon Treaty.
This means the Prime Minister can start the formal leaving negotiations between the UK and the EU.
Ministers were forced to table legislation after the Supreme Court upheld an earlier ruling that the Government must obtain the approval of Parliament before it could begin negotiating Britain's withdrawal from the EU.
Article 50 forms part of the Lisbon Treaty – signed by all members of the European Union (EU) in December 2007 – and sets out the rules or the process of a member state leaving the EU.
Theresa May told the Conservative Party Conference in October that Article 50 would be triggered by the end of March 2017.
Once that happens, the process of leaving is underway. A two-year negotiation period on Britain’s future relationship with the EU will then begin.
How are MPs likely to vote?
The Bill is expected to clear its first parliamentary hurdle relatively easily as Labour's leadership is backing it, despite the Liberal Democrats and Scottish National Party set to vote against it.
If the government win then it will then return to the Commons next week for the committee stage when the real parliamentary battle is expected to take place.
Opposition parties are expected to attempt to push through a series of amendments to the bill.
The Government has kept the Bill to just two tightly-drawn clauses in an attempt to limit the scope for amendments.
The Government remain confident that the Bill will complete its passage through Parliament including the House of Lords in time for the Prime Minister to meet her March 31 deadline for invoking Article 50.
Mrs May said MPs would face a very clear choice when they came to go through the division lobbies on Wednesday.
Speaking from Dublin on Monday she said: "The people of the United Kingdom voted on June 23 last year. They voted in a referendum that was given to them overwhelmingly by Parliament".
"The people spoke in that vote. The majority voted to leave the European Union. I think it is now the job of the Government to put that into practice.
"I hope that when people come to look at the Article 50 Bill they will recognise it is a very simple decision: do they support the will of the British people or not?"
Brexit Secretary David Davis, who will pilot the Bill through the Commons, said: "It is not a Bill about whether or not the UK should leave the EU, or how it should do so.
"It is simply about implementing a decision already made, a point of no return already passed. We asked the people of the UK if they wanted to leave the EU; they decided they did."
Jeremy Corbyn is facing a revolt by some Labour MPs, over his decision to impose a three-line whip ordering them to vote for the Bill at second reading.
Shadow ministers Jo Stevens and Tulip Siddiq quit in protest, and other frontbenchers have said they will oppose the Bill, even if it costs them their jobs.