The Act's long title is To Confer power on the Prime Minister to notify, under Article 50(2) of the Treaty on European Union, the United Kingdom's intention to withdraw from the EU.

The Act's first reading as a bill in Parliament was on 26 January 2017, after the Supreme Court, in the Miller case, dismissed the government's appeal against the High Court's declaratory order, dated 7 November 2016, that "The Secretary of State does not have power under the Crown's prerogative to give notice pursuant to Article 50 of the Treaty on European Union for the United Kingdom to withdraw from the European Union.

[15] Topics covered by the amendments submitted by MPs and selected for debate at the Committee stage included: Parliamentary scrutiny, the devolved administrations (Wales, Scotland and Northern Ireland), and the status of citizens of the EU and the European Economic Area (EEA) (and also that of Swiss nationals) in the UK, and that of expatriate British citizens in other parts of the EU and the EEA outside the UK (and also in Switzerland).

On 17 February 2017 the House of Commons Library issued a briefing paper on "Parliament's role in ratifying treaties", which quoted David Jones, Minister of State for Exiting the EU, as confirming in the debate the government's commitment to bringing forward a motion, for the approval of both Houses, that will cover the withdrawal agreement and the future relationship with the European Union, and as stating that the government expected and intended this will be before the European Parliament debates and votes on the final agreement.

[20] "Within three months of exercising the power under section 1(1), Ministers of the Crown must bring forward proposals to ensure that citizens of another European Union or European Economic Area country and their family members, who are legally resident in the United Kingdom on the day on which this Act is passed, continue to be treated in the same way with regards to their EU derived-rights and, in the case of residency, their potential to acquire such rights in the future."

In the second reading debate, one of the cross bench peers, Lord Hope, who had been a Supreme Court Justice from 2009 until his retirement in 2013, mentioned that the wording of the bill sufficed for giving notice of withdrawal, as the Supreme Court's decision in the Miller case required, but it said nothing about the process of the two further stages stated in article 50: negotiation, and the concluding of an agreement between the Union and the state that was withdrawing.

[24] The amendment adds to the bill a requirement that the government will introduce proposals within three months of the withdrawal notification to ensure EU citizens in the UK have the same residence rights after Brexit as before.

[28] The report stated that if there is no post-Brexit deal at the end of the two-year negotiating period, the UK could withdraw without payment of a "divorce bill" to the EU.

Lord Forsyth of Drumlean, opposing the amendment, compared it to Gulliver, in trying to tie down the Prime Minister—by hair, arms and legs—in order to prevent her from getting an agreement for the UK before leaving the European Union.