MPs have rejected Theresa May’s EU withdrawal agreement on the day the UK was due to leave the EU.
The government lost by 344 votes to 286, a margin of 58.
It means the UK has missed an EU deadline to delay Brexit to 22 May and leave with a deal.
The prime minister said the UK would have to find “an alternative way forward”, which was “almost certain” to involve holding European elections.
Thousands of Leave supporters gathered outside Parliament to protest against the delay to Brexit, bringing traffic to a standstill
Mrs May now has until 12 April to seek a longer extension to the negotiation process to avoid a no-deal Brexit on that date.
With a clear majority in the Commons against a no-deal Brexit, and with MPs holding more votes on alternative plans on Monday, Mrs May said that the UK would have to find “an alternative way forward”.
The prime minister said that the outcome was “a matter of profound regret”, adding that “I fear we are reaching the limits of this process in this House”.
Downing Street said it was still not an “inevitability” that the UK would have to take part in elections to the European Parliament in May.
