Opposition politicians, however, insisted that the government must recall Parliament.
The highest civil court in Scotland has ruled Boris Johnson's suspension of Parliament is unlawful, in the latest setback for the UK Prime Minister.
But Johnson's decision is controversial because it would leave parliament without a voice for five weeks in the run-up to Brexit, with the divorce terms still in doubt.
"We are calling for parliament to be recalled immediately", said Scottish National Party lawmaker Joanna Cherry, who led the legal challenge, after Scotland's Court of Session ruled the prorogation should be annulled.
If Boris Johnson is found to have deceived the Queen he should quit, a former Tory MP has said.
A UK government spokesperson said after the court ruling: "We are disappointed by today's decision, and will appeal to the UK Supreme Court".
Still, a group of opposition lawmakers gathered outside the 800-year-old Palace of Westminster demanding its recall.
"Although Johnson claimed he was shutting down Parliament for five weeks to work on his legislative agenda", NPR's Frank Langfitt reports from London, "most political observers think he was trying to sideline legislators so they couldn't blockhis plan to crash the United Kingdom out of the European Union without a withdrawal agreement".
In a speech that is at odds with the stance of Labour's leader Jeremy Corbyn, Watson will say there is "no such thing as a good Brexit deal" and Labour must campaign unequivocally to remain, the BBC said. The court was shown documents that showed Johnson was considering prorogation weeks before he asked Queen Elizabeth to suspend the legislature.
Buckingham Palace declined to comment on the ruling, saying it was a matter for the government.
Dominic Grieve, one of 21 Brexit rebels thrown out of Johnson's Conservative Party last week, said that if Johnson had misled the queen, he should resign.
Opponents argued that the real reason was to shut down debate and challenges to his Brexit plans.
The court heard the prime minister was sent a note on 15 August asking if he wanted to prorogue parliament from mid-September.
But the five-week suspension also gives him a respite from rebellious lawmakers as he plots his next move to break the political impasse over Brexit and lead Britain out of the European Union by October 31, "do or die".
"This was an egregious case of a clear failure to comply with generally accepted standards of behaviour of public authorities", concluded one judge, Philip Brodie, according to a summary of the court verdict.
The decision overturned last week's ruling that courts did not have the power to interfere with political matters such as the proroguing of Parliament. 'A general election might well fail to solve this Brexit chaos'. The UK is due to leave the European Union on 31 October.
"I think it's disappointing that the courts are trying to interfere in the way the country is run", he said. Its leader Nigel Farage took out newspaper ads Wednesday, offering an electoral pact with the Conservatives if Johnson backed a "clean break" - a no-deal Brexit.
But Johnson's office said "the PM will not be doing a deal with Nigel Farage".