The Act was one of a number of planned pieces of legislation affecting international transactions and control of borders, including movement of goods.

An analysis of the process set out in the Act published by the Institute for Government discusses the procedure for approving treaties that is set out in the Constitutional Reform and Governance Act 2010 (CRAG) which may apply to the withdrawal agreement and the framework agreement for future relations, depending on what they contain.

[12] Alternatively (section 13 (10)), if by Monday 21 January 2019 – less than eleven weeks before the mandatory negotiating period ends on Friday 29 March – there is no agreement in principle in the negotiations on the substance of the withdrawal arrangements and the framework for the future relationship between the EU and the United Kingdom, the government must publish a statement setting out how the government proposes to proceed, and must arrange for debate about that in Parliament within days.

The Government recognises that it is open for Ministers and members of the House of Commons to table motions on and debate matters of concern and that, as is the convention, parliamentary time will be provided for this."

The Act makes explicit in section 5 that the Charter of Fundamental Rights of the European Union will cease to be a part of UK law after Brexit.

[20] In addition, there are specific interpretative exceptions for the rule in Francovich[21] (which allows compensation for not transposing EU directives into domestic law), and the Charter of Fundamental Rights of the European Union.

[25][26] The government published in March 2018 a provisional analysis about the devolved administrations receiving new powers as the UK leaves the EU.

[31] The Scottish Parliament passed the UK Withdrawal from the European Union (Legal Continuity) (Scotland) Bill 2018 on 21 March 2018,[32] to prepare Scots law for Brexit, but was referred for scrutiny to the Supreme Court under section 33 of the Scotland Act 1998, to determine whether the parliament had legislative competence to pass such a bill;[33][34] pending that judgement, Royal Assent was not sought.

The (UK) Secretary of State for Scotland, David Mundell, said the court had "provided much-needed legal clarity" that the bill "goes beyond the powers of the Scottish Parliament", but Scotland's Brexit Secretary Michael Russell argued that the UK government had "changed the rules of the game midway through the match" in an "act of constitutional vandalism".

[40] Following a second general election in 2022, Sir Jeffrey Donaldson, DUP leader and Member of Parliament for Lagan Valley secured an MLA position in the eponymous constituency, becoming the presumed choice for Deputy First Minister, but announced that the DUP leadership team would decide if he would take that seat, (and thus call a by-election for his Westminster seat).

[41] The DUP refused to assent to the election of a Speaker, in further protest to the Northern Ireland Protocol, so the Assembly could not continue to other business including the appointment of a fresh executive.

[44] After a meeting to discuss the latest development of the negotiations, when the European Union's chief negotiator Michel Barnier repeatedly told the Prime Minister the EU would not agree to discuss trade until an agreement was found on the terms of withdrawal, the prime minister informed the House of Commons on 2 July 2018 that she warned EU leaders that she did not think Parliament will approve the withdrawal agreement in the autumn "unless we have clarity about our future relationship alongside it".

[45] This was followed by a decision at a Cabinet meeting at Chequers on 6 July that continuing preparations for potential outcomes included the 'no deal' possibility.

[46] David Davis, who as Secretary of State for Exiting the European Union had introduced the Act as a bill in Parliament, and who had attended the Cabinet meeting at Chequers on 6 July, resigned on 8 July,[47] saying in his resignation letter, "In my view the inevitable consequence of the proposed policies will be to make the supposed control by Parliament illusory rather than real.

[49] Later in the day, the resignation of the Foreign Secretary, Boris Johnson, who had also attended the Chequers Cabinet meeting, was made public.

[52] The government's policy on the future relationship between the United Kingdom and the European Union that the Cabinet had discussed at Chequers was published as a White Paper on 12 July 2018[53] for debate in the House of Commons the following week.

[55] The government confirmed in the House of Commons on 19 July 2018 that the UK would be leaving the EU on 29 March 2019, as stated in the Withdrawal Act and the White Paper.

[citation needed] The first meeting of Dominic Raab, the newly appointed UK Secretary of State, with the EU's chief negotiator, Michel Barnier, was in Brussels later on the same day (19 July 2018).

Redrafting all of the tens of thousands of laws affected and voting on them through Parliament would be an impossibly time-consuming process, so the bill included provisions, informally known as Henry VIII clauses, which would allow ministers to make secondary legislation to amend or remove these laws (both primary and secondary legislation) to resolve "deficiencies" by making statutory instruments.

Although some safeguards were included to limit the situations in which law can be modified, for instance with the inclusion of sunset clauses, the provisions granting these powers were criticised for being too wide-ranging.

On 13 July 2017, David Davis, the Secretary of State for Exiting the European Union, introduced the bill in the House of Commons.

[69] The committee stage was originally scheduled to take place after MPs returned to Parliament following the conclusion, in October, of their respective party conferences.

[112] A government-backed amendment allowing legal challenges on the basis of EU law for the three-year period following Brexit also passed.

[115][116] That day the Lords agreed to accept the government's EU Withdrawal Bill, thus paving the way for it to become law upon royal assent.