MPs have voted by 413 to 202 – a majority of 211 – for Prime Minister Theresa May to ask the EU for a delay to Brexit.
It means the UK may not now leave on 29 March as previously planned.
Mrs May says Brexit could be delayed by three months, to 30 June, if MPs back her deal in a vote next week.
If they reject her deal again then she says she will seek a longer extension – but any delay has to be agreed by the 27 other EU member states.
Political Correspondent Jonathan Blake explains what happens next.