However, both the Tories and Labour have ruled out the possibility of a referendum on the subject and time to change their minds is running out.
Sir Patrick claimed the characters in his most famous screen roles, Star Trek's Captain Jean-Luc Picard and Charles Xavier from the X-Men, would have supported Britain's European Union membership.
Sir Patrick, 77, was joined by MPs from across the political spectrum as he opened a People's Vote rally attended by more than 1,200 people in London.
"That is why I support a people's vote on the final deal".
Nine grassroots anti-Brexit groups have joined forces in the new campaign which is demanding a public final say on the eventual Brexit deal Prime Minister Theresa May reached with Brussels.
Speaking to the BBC at the event, Labour peer Lord Adonis said: "People want a say..."More news: A Bushfire Still Burning in Sydney's West is Being Treated as Suspicious
"No-one had any idea what the consequences of Brexit were going to be".
During a speech to the crowd, Green Party MP Caroline Lucas will say: 'We will be making the case in Parliament, but this is too big and too important to be determined exclusively by politicians.
Green MP Caroline Lucas will say: "We will be making the case in Parliament, but this is too big and too important to be determined exclusively by politicians".
Conservative MP Anna Soubry told the crowd the United Kingdom was about to embark on a course that would "make you and your grandchildren... less prosperous than you are now".
"Whether you think the government will negotiate a good deal or bad deal, Brexit is definitely a big deal", Open Britain's Executive Director James McGrory said in a statement.
He said: "The campaign for the People's Vote is simply requesting that we have another chance to consider what the terms of this divorce are going to be".More news: Three funerals for victims of Humboldt crash on Friday
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.
Stewart, who portrayed psychic Professor Charles Xavier in the Hollywood series after finding global 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.
He argued that Britain could "simply stay" in the European Union if the exit deal was rejected in a fresh referendum.
"We are short on time, but we have people power on our side".
X-MEN leader Professor X and Star Trek's Captain Jean-Luc Picard would have voted Remain, according to the actor who played the roles.
"(We) will be able to boldly go again to areas that perhaps we have neglected. friendly wonderful places where we can renew old friendships, rebuild relationships and develop fantastic new free trade deals".More news: BCI asks Jammu, Kathua bar bodies to call off strike