MPs and peers will return to Parliament later after the Supreme Court ruled that its suspension was unlawful.
Boris Johnson is returning early from a UN summit in New York, while Labour cut its conference short in the wake of Tuesday's unanimous ruling.
The PM, who has faced calls to resign, has said he "profoundly disagreed" with the decision but would respect it.
Commons Speaker John Bercow has said there will be "full scope" for urgent questions and ministerial statements.
- EU watches and waits amid UK turmoil
- Suspending Parliament was unlawful, court rules
- And what happens now?
On Tuesday, the court ruled it was impossible to conclude there had been any reason - "let alone a good reason" - to advise the Queen to prorogue Parliament for five weeks in the run-up to the Brexit deadline of 31 October.
Mr Johnson, who was attending the UN General Assembly in New York, spoke to the Queen after the ruling, a senior government official said, although no details of the conversation have been revealed.
The prime minister also chaired a 30-minute phone call with his cabinet.
A source told the BBC the Leader of the Commons, Jacob Rees-Mogg, said to cabinet ministers on the call that the action by the court had amounted to a "constitutional coup".
What will the PM do now?
"He has completely lost control of the process."
That's how one of the prime minister's cabinet colleagues summed up Boris Johnson's position as he flies back to face Parliament.
Mr Johnson's likely to end up at the despatch box on Wednesday, where he will have the rulings of the Supreme Court brandished at him.
The opposition parties calling on him to quit. A flurry of urgent demands for the government to answer questions about its plans for Brexit. And all that before the profound embarrassment of having been found to have broken the law.
Downing Street at this stage seems to have no intention of doing anything other than toughing this out.
Speaking after the ruling, Mr Johnson insisted the suspension of Parliament had been necessary in order for him to bring forward a Queen's Speech on 14 October outlining his government's policies.
But critics said he was trying to stop MPs scrutinising his Brexit plans and the suspension was far longer than necessary.
During a speech in New York, Mr Johnson said he "refused to be deterred" from getting on with "an exciting and dynamic domestic agenda" and to do that he would need a Queen's Speech.
The court ruling does not prevent him from proroguing again in order to hold one, as long as it does not stop Parliament carrying out its duties "without reasonable justification".
A No 10 source said the Supreme Court had "made a serious mistake in extending its reach to these political matters" and had "made it clear that its reasons [were] connected to the Parliamentary disputes over, and timetable for" Brexit.
But Supreme Court president Lady Hale emphasised in the ruling that the case was "not about when and on what terms" the UK left the EU - it was about the decision to suspend Parliament.
The decision led Labour leader Jeremy Corbyn to bring forward his speech at the Labour Party conference in Brighton from Wednesday to Tuesday so that he could return to Westminster.
Speaking to a crowd of cheering delegates, Mr Corbyn said: "The government will be held to account for what it has done. Boris Johnson has been found to have misled the country. This unelected prime minister should now resign."
The calls for Mr Johnson to resign were echoed by Scotland's First Minister, the SNP's Nicola Sturgeon, Wales' First Minister, Labour's Mark Drakeford, and Sinn Fein's vice president, Michelle O'Neill.
But Mr Johnson was backed by US President Donald Trump at a joint press conference at the UN summit.
"I'll tell you, I know him well, he's not going anywhere," said Mr Trump, after a US reporter quizzed the prime minister on whether he was going to resign.
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