Hundreds of supporters of the campaign were at the rally in Camden, north London, to hear speeches from Sir Patrick, Ms Soubry, Mr Umunna, Lib Dem MP Layla Moran and Caroline Lucas, a co-leader of the Green Party.
Organisers said about 1200 people were at the event, including MPs from all leading parties.
'And why? Because unity, common cause, wellbeing of society and debate were paramount to belief of this fictional character.
The actor is expected to join about 1,000 campaigners for the rally in a bid to attract support from people who oppose Brexit from across the political spectrum.
'Since the 2016 referendum, there has been a concerted effort by many - including government - to shut down debate about Brexit and to tell us that we should simply trust ministers to get on with it because Brexit is an irreversible process. 'Our country's future is at stake and we will not stand idly by, ' he said. It was a vote in the dark two years ago.
He said Brexit would allow Britain to "boldly go" to areas it has neglected in the search for new free trade deals. "This issue is far too important to leave to the politicians".
Stewart, who portrayed psychic Professor Charles Xavier in the Hollywood series after finding worldwide fame as the Star Fleet captain, appeared on the BBC's Andrew Marr Show yesterday as he prepared to launch the People's Vote campaign group.
D Edith Charles
"We'll do everything we can in Parliament for a people's vote".
Meanwhile, pro-Brexit demonstrators also turned up at the launch, and Conservative MP Nadine Dorries argued there was no public appetite for a second referendum.
He said: "The cost of war was everywhere and many never recovered from it. The public don't want it". What I am motivated by is history and emotion. "So the day we joined was one of the most exciting days of my adulthood", he added.
Of respondents who voted to leave the European Union, 45% were opposed to the idea of a public vote, compared to 38% in favour.
Foreign Secretary Boris Johnson countered with a Star Trek allusion of his own, promising that Britain's departure from the European Union will allow it "to boldly go again to areas that perhaps we've neglected over the last 45 years".
Sir Patrick Stewart has declared that two of his most famous characters would have voted Remain, as he helped launch a campaign for a referendum on the final Brexit deal.
"We are short on time, but we have people power on our side".