But Johnson will have to wait until early next week to hear the judgment of the Supreme Court, the highest court in Britain.
"I think we are making some progress", Johnson said in a broadcast clip, adding that European Commission President Jean-Claude Juncker's saying on Wednesday that he was not "emotionally attached" to the Irish backstop was encouraging.
Sterling hit a two-month high versus the dollar on Juncker's comments, rising to US$1.2546, its highest since July 19.
For three days, top lawyers representing both sides have weaved their way through a maze of legal cases to contend respectively.
Before the suspension, Johnson suffered one defeat after another in Parliament, where he has no majority.
This week the minority Liberal Democrats have been holding their annual rally in Bournemouth. "I have asked the prime minister to make, in writing, alternatives".
It means the Commons would have in any case been shut until early October.
His opponents say the real reason was to prevent members of parliament (MPs) from thwarting his plans.
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Pannick said he wanted a declaration from the court that the advice to the monarch was unlawful and that parliament should reconvene to decide how to proceed.
During the hearing, the court was shown a handwritten note in which Johnson had described the parliamentary session as "a rigmarole.to show the public that MPs were earning their crust".
"There is no other rational reason for the length of the prorogation", he said, adding that would amount to an improper objective.
In one of the forceful presentations, barrister Aidan O'Neill told the 11 judges: "What we have with this prorogation is the mother of parliaments closed down by the father of lies".
Major, who was prime minister from 1990 to 1997, told the court in a 10-page written submission: "The current factual picture, on the material which is available and with regard to the absence of evidence which ought to be available but has not been provided, is deeply concerning".
Opponents of the government claim Johnson unlawfully shut Parliament until October 14 to prevent lawmakers from scrutinizing his plan to take Britain out of the European Union at the end of next month, with or without a divorce deal.
He said that in such circumstances, a prime minister opposed to a standing army could prorogue in order to disband the military, or suspend Parliament ahead of facing a vote of confidence vote.
If the court rules that the suspension was illegal, Johnson could be forced to call lawmakers back to Parliament immediately.
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Critics both inside and outside of parliament also have contended that the shutdown was geared to stymie debate in parliament about Brexit.
Juncker said he had a "rather positive" meeting with Johnson in Luxembourg on Monday and still thought a deal could be done before the October 31 Brexit deadline. But does Johnson even want a deal?
He is now racing to try to agree a deal with Brussels to meet his October 31 deadline - although European Union leaders say he has yet to offer formal proposals.
Mr Juncker went on to confirm he is "doing everything to have a deal" because he wanted to ward off a no-deal with "catastrophic consequences".
The EU confirmed it had received new documents from Britain relating to ways of maintaining an open border between EU member Ireland and the U.K.'s Northern Ireland - the key sticking point to a deal.
"As far as the so-called alternative arrangements are concerned, allowing us and Britain to achieve the main objectives of the backstop ... if the results are there, I don't care about the instrument", he said.
"Whilst we seek a deal, we recognize we may not be able to agree a deal and in that instance we will leave with no deal", he said.
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