MPs are debating whether to back the PM’s plan for the UK to leave the EU on 31 January, ahead of a vote later.
The EU (Withdrawal Agreement) Bill would also ban the government from extending the transition period – where the UK is out of the EU but follows many of its rules – past 2020.
Boris Johnson said it would allow the UK to “move forward”.
But Jeremy Corbyn said Labour would oppose the bill, and there was “a better and fairer way” to leave the EU.
The government has insisted a trade deal with the EU can be in place by the end of the transition period, but critics say this timetable is unrealistic.
The result of the Commons vote is expected at about 15:00 GMT.
The withdrawal bill, which would implement the Brexit agreement the prime minister reached with the EU in October, was introduced in Thursday’s Queen’s Speech, setting out the government’s priorities for the next year.
Beginning the debate in the Commons, the prime minister said his bill “learns the emphatic lesson of the last Parliament” and “rejects any further delay”.
“It ensures we depart on 31 January. At that point Brexit will be done. It will be over,” he told MPs.
“The sorry story of the last three years will be at an end and we can move forward.”
Mr Johnson said it also “paves the way” for a “ambitious free trade deal” with the EU.
The bill’s second reading is the first chance MPs have had to debate its main principles in the House of Commons.
With the Conservatives having won an 80-seat majority at last week’s general election, the bill is expected to pass easily, before it moves on to further scrutiny by MPs and the House of Lords.
MPs have been given a further three days – 7, 8 and 9 January – to continue their debate.
The government says it will get the bill into law in time for the 31 January Brexit deadline.
There are changes to the previous bill, which was backed by the Commons in October, but withdrawn by the government after MPs rejected a three-day deadline for getting it through Parliament.
The changes include:
- Legally prohibiting the government from extending the transition period – during which a trade deal between the UK and EU will be discussed – beyond 31 December 2020
- Allowing more UK courts to reconsider European Court of Justice rulings that have been retained in UK law after Brexit
- Requiring ministers to report annually to Parliament on disputes with the EU under the prime minister’s withdrawal agreement
- Repealing spent legislation that “now serves no purpose”
The bill also loses a previous clause on strengthening workers’ rights.
The government now says it will deal with this issue in a separate piece of legislation, but the TUC has warned that the change will help “drive down” working conditions.