The woman behind the Supreme Court legal challenge against triggering Brexit without parliamentary approval said that a Commons motion on the issue is "irrelevant" and a "red herring".
Gina Miller said a vote in favour of a Labour amendment calling on the Government to publish its Brexit plan before triggering Article 50 by the end of March 2017 was not legally binding.
"The motion is to set up a timetable, it actually doesn't say anything about the contents (of the Brexit negotiations)," Ms Miller said.
"The inference was that that motion - having passed in the Government's favour - that we should basically pack up and go home, because that's Parliament taking responsibility and looking after itself.
"And we would argue no, it's actually a red herring in that it's a political move, it's not a legal one," she added.
MPs backed a motion on Wednesday that calls on the Government to publish its Brexit plan and trigger Article 50 of the Treaty on European Union before March 31 by 448 votes to 75.
It came a day before the Supreme Court case came to a close and a ruling is set to be issued in January.
Brexit Secretary David Davis said that while the Government will set out its "strategic plans" before launching the formal mechanism for withdrawal from the EU, it will not reveal anything which might "jeopardise our negotiating position".
Ms Miller said it was important to recognise that a motion does not hold the same weight as an Act of Parliament.
She added: "A motion or a resolution are irrelevant to our case. Our case is simply that only primary legislation, only an Act of Parliament, will do."
The Supreme Court heard an appeal launched by the Government against a unanimous High Court ruling that said the Prime Minister does not have the power to bypass MPs by relying on the royal prerogative to trigger Article 50.
The ruling would mean that lawmakers would have the opportunity to table amendments to make Theresa May reveal more about her negotiating strategies and priorities before triggering the two-year period of divorce negotiations with the 27 other countries in the EU bloc.
But Ms Miller said that she was optimistic that the ruling would be in her favour.
She said: "I don't feel that they put up as strong an argument as they could have, possibly. So it's all a little baffling, and their arguments were quite circular rather than (having) any sort of real depth to them.
"I don't believe that the Government have really addressed the central legal arguments that we won on in the High Court, so we're feeling fairly confident."
In response to the comments, a Government spokesperson said: "The country voted to leave the European Union in a referendum provided for by an Act of Parliament. We are determined to respect the will of the British people and intend to trigger Article 50 by the end of March next year.
"Last week, Parliament indicated its support for the Government's timetable. As our position in the Supreme Court Appeal made clear, we do not believe another Act of Parliament is necessary."