The ruling unanimously passed by 11 Supreme Court judges further weakened Johnson's grip on power and gave Parliament more room to prevent him from leading Britain out of Europe next month.
Johnson, in New York, said he would respect the Supreme Court's decision to suspend parliament, but "strongly disagreed" that the setback would not affect his exit agenda.
The Supreme Court's ruling, the most important constitutional law ruling in decades, strongly condemned Johnson's actions. Opposition leaders demanded that Johnson resign immediately because he misled the Queen. Earlier, the Queen approved the adjournment of Parliament on his proposal.
"The decision to recommend that the Queen adjourn Parliament is illegal because it impedes the ability of Parliament to perform its constitutional functions without justification," said Brenda Hale, President of the Supreme Court.
The ruling pointed out that Johnson did not give any reason for parliament to adjourn for five weeks - "let alone a good reason". Johnson's decision to adjourn Parliament had an "extreme" effect on the cornerstone of British democracy.
"The Prime Minister's advice to the Queen is illegal, null and void and has no legal effect," Hale said, adding that the parliament has not adjourned, and what to do next will be decided by the Speakers of both houses.
The Speaker of the House of Commons said the House of Commons would meet Wednesday at 1030 GMT.
When Johnson stood with President Trump at the United Nations General Assembly, he was asked whether he would resign. "No, no, no," Johnson answered, Trump interposed. "I tell you, I know him well, and he's not going anywhere."
A government official said Johnson spoke to Queen Elizabeth by telephone after the ruling was announced.
Asked if the call was an apology, the official refused to discuss the content.
Johnson will return to Britain after speaking at the United Nations General Assembly.
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