MPs will vote later on whether to back the prime minister’s plan for the UK to leave the EU on 31 January.
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”.
Opponents say the bill leaves the UK’s future uncertain, and agreeing a trade deal with the EU could take many years.
But the government insists one can be in place by the end the transition period.
The result of the Commons vote on the bill 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 oven is on, it is set at gas mark four, we can have it done at lunchtime and the new deal I negotiated will restore our great institutions,” he said.
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 in the Commons.
The government says it will get the bill into law in time for the 31 January Brexit deadline.
An earlier withdrawal agreement – reached between previous Prime Minister Theresa May and the EU – was rejected three times by MPs.