Prime Minister Theresa May's Conservative government lost its appeal on Tuesday against a surprise High Court decision in November that ruled the government could not trigger Brexit negotiations without the backing of MPs in parliament.
The ruling by 11 justices resolved once and for all the row over who has the right to trigger Article 50 and start Brexit negotiations.
Lord Neuburger read out the ruling at around 9.30 to a packed court room. He revealed that judges ruled by a majority of 8 to 3 that the government could not trigger Article 50 to begin Brexit negotiations without the backing of parliament."
So MPs will now get the chance to vote.
Reacting to the verdict the main complainant against the government Gina Miller said: "Only parliament can grant rights to British people and only parliament can take them away...Parliament alone is sovereign."
A spokesman for a group representing expats was also "delighted and relieved" with the ruling.
"We are the people most profoundly affected by all of this," he said. "Everything that British citizens take for granted rests on being EU citizens."
In a separate decision however judges ruled the government did not have to consult parliaments in Scotland, Wales and Northern Ireland before triggering Article 50.
The government said it was disappointed by the result but will comply with it.
Neuburger had earlier stressed that their ruling had nothing to do whether or not Britain should leave the EU or how the Brexit negotiations should be managed, but only on whether the government or parliament should trigger the divorce negotiations.
While "Bremainers" will cheer the verdict, experts see the landmark ruling as slowing down the process of Brexit rather than putting a halt to it.
British PM Theresa May has been severely criticized for trying to bypass parliament and for keeping her cards close to her chest on her negotiation strategy.
(A lone protester outside the Supreme Court on Tuesday. AFP)
Tuesday's eagerly awaited Supreme Court verdict should force her to reveal more to parliament about her planned Brexit strategy.
The legal dispute centred around the famous Article 50 of the treaty of the European Union, which must be triggered for Britain to begin the official and painstaking process of divorce from the EU.
The government believed it had the right to officially inform Brussels it is leaving the EU via its royal prerogative – powers that technically belong to the Queen, but which are vested in the government. But lawyers for the claimants, two British citizens, and other interested parties argued that parliament must have the right to decide.
Theresa May has said previously that the government would trigger Article 50 to begin formal exit negotiations by the end of March 2017, however Tuesday's decision may scupper that plan.
A date must now be set for the momentous parliamentary vote.
Once Article 50 is triggered a two year process of negotiations between the UK and the EU, will begin in earnest, although many experts believe talks will rumble on for much longer.