The European Union (Notification of Withdrawal) Bill will have its final debate and vote later tonight to allow the Prime Minister to invoke Article 50 of the Lisbon Treaty to begin a two-year period of negotiations for the UK's new deal as a non-member of the European Union (EU) by 2019.
The Commons will debate the last set of amendments to the bill, including on key principles for the negotiation process, before the bill goes to its third and final reading for the vote.
The Opposition Labour leader Jeremy Corbyn has instructed his MPs to vote in favour of the bill whether any amendments are made or not.
However, he is set for another round of party rebellion after over 40 MPs had defied the whip at the last vote earlier this month.
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Mayherself faces a rebellion of up to a dozen of her Conservative MPs, who are expected to defy the party's whip and vote for the rights of EU citizens living in the UK to be guaranteed before Brexit negotiations begin.
Keir Starmer, the shadow Brexit secretary, welcomed this as an important concession but others have dismissed it as a "take it or leave it" offer.
The government is expected to win the final voting round, later today.
Once the bill passes the Commons, it will be debated in the House of Lords after it returns from recess on February 20, where it is expected to be given the final nod.
The bill was tabled last month after the Supreme Court ruled that MPs and peers must have a say before Article 50 of the Lisbon Treaty could be triggered.
David Davis,UK minister for exiting the European Union, had opened the debate in the House of Commons with a clear message to MPs that they mustimplement a decision made by the people in the June 2016 referendum - with 51.9 per cent wanting to leave the EU and 48.1 per cent wanting to remain within the 28-nation economic bloc.