Peers voted 272 to 169 in favour of a cross-party motion that will force a government minister to make a series of statements in parliament in October.
That would make it difficult for the next prime minister to prorogue parliament in the run-up to the UK leaving the EU on 31 October – the current Brexit deadline.
The government opposed the Lords’ amendment but was heavily defeated, with 13 Conservative peers rebelling to vote with the opposition parties.
The draft law will now pass to the House of Commons, where a knife-edge vote is expected when it is debated on Thursday.
The House of Lords motion, tabled as an amendment to the Northern Ireland bill, builds on a similar plan put forward in the Commons by former attorney general Dominic Grieve last week. That proposal passed by a single vote, and would require ministers to produce regular reports on efforts to restore power-sharing at the Northern Ireland assembly.
The Lords amendment ensures that this must take place in parliament, rather than simply in written form. The move is designed to ensure that parliament is sitting throughout October, in the run-up to the Brexit deadline.
Reports earlier this week suggested Mr Johnson’s team were mulling over a plan to hold a Queen’s Speech in early November and suspend parliament for the preceding two weeks.
The latest motion was tabled by crossbench peer Lord Anderson, Labour’s Lord Goldsmith, the Liberal Democrats’ Lord Newby and Conservative former cabinet minister Viscount Hailsham. Lord Anderson told peers the amendment would “express parliament’s expectation of being consulted not just on these reports but on an even more pressing political issue: the future of our relationship with the European Union”.
He said: “If parliament were to endorse a no-deal Brexit, as it has not done to date, then there could be no democratic argument against it. But for that decision to be left to our next prime minister, elevated to that office by members of his own party and freed from any requirement to obtain the consent of parliament, would be another matter altogether.”
He said it was “extraordinary” that Mr Johnson had refused to rule out proroguing parliament. Responding for the government, Lord Duncan said that passing the amendment would give the wrong impression “that we can use Northern Ireland for different purposes when we choose to do so”.
He told the Lords: “The key thing right now is to keep us focused on the important aspect of this, which is the delivery of an executive in Northern Ireland. That must be our principle aim.” He asked for the amendment to be withdrawn, but the peers proposing it declined and it was comprehensively approved.
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