He insisted the EU had made unfair demands to "exert leverage" in Brexit trade talks, including threats to block food exports, and said the Internal Markets bill would prevent European negotiators from taking an "extreme and unreasonable" stance on the withdrawal agreement.
Johnson won the second reading parliamentary vote on the Internal Market Bill by 340 votes to 263, but some 30 of his MPs abstained and two voted against the bill.
The Bill aims to end the legal legitimacy of the Northern Ireland protocol - contained within the Withdrawal Agreement - in areas such as customs and state aid and financial assistance.
Speaking to reporters on Monday morning, Mr Cameron said: "Passing an act of parliament and then going on to break an worldwide treaty obligation is the very, very last thing you should contemplate".
Several of Johnson's own Conservative MPs expressed alarm about breaking global law, with ex-finance minister Sajid Javid and former attorney general Geoffrey Cox among those saying beforehand that they would not back the bill as it stood. "I believe the United Kingdom's word is its bond and I think this is damaging our global reputation for honesty and straight-dealing", Sir Roger said. "There is much to play for yet".
"Absurd and self-defeating as that action would be...the European Union still have not taken this revolver off the table", he told MPs.
Summing up the reading before MPs went to vote, Cabinet Office Minister Michael Gove said that the United Kingdom is committed to making a success of its negotiations with the EU.
"We're committed to making a success of those negotiations. Those negotiations go on", Mr Gove told the Commons.
With Starmer self-isolating after being told this morning that a member of his household was showing possible symptoms of Covid-19, the Shadow Business Secretary and former party leader opened the debate for Labour.
"Either he wasn't straight with the country about the deal in the first place or he didn't understand it", Miliband said.
"When it comes to preserving the integrity of the United Kingdom and clearly delivering for the people of Northern Ireland when it comes to the Good Friday Agreement, we've said from day one. that we would always stand by our word and not compromise when it comes to unfettered access in goods and services but also standing by the Good Friday Agreement", she said on BBC Breakfast.
"Because a competent government would never have entered into a binding agreement with provisions it could not live with".
As the Government's internal markets bill passed the first vote in the Commons last night, James O'Brien branded the news an "astonishing U-turn".
"I will therefore regretfully be unable to support the bill at its second reading and urge the government to amend it in the coming days".
"It is critical that we pass this Bill before the end of the year".