A new campaign group, backed by a star from the Star Trek movies, was launched Sunday calling for a public vote on a final Brexit deal.
Mr Johnson addressed the remarks made by Sir Patrick, who also played the role of Captain Jean-Luc Picard in Star Trek: The Next Generation.
The People's Vote brings together nine anti-Brexit groups which claim to have one million members behind a single campaign message.
The campaign aims to persuade people to back a public vote on the terms agreed between the United Kingdom and European Union when talks come to a close later this year.
The rally at the Electric Ballroom attracted support from the Conservatives' Anna Soubry, Labour's Chuka Umuna, Liberal Democrat's Layla Moran and the Green Party's only MP Caroline Lucas.
The Individuals's Vote marketing campaign is demanding the British public be given the ultimate say on the deal secured by Prime Minister Theresa May, slightly than MPs in Parliament.
"Brexit is not inevitable".
"Brexit will affect everybody in the country, which is why it should not be left to 650 politicians to decide our future but 65 million people".
An internet ballot from Opinium revealed to mark the launch suggests greater than half of the British public (52%) backs a vote on the ultimate deal, with 31% opposed.
But he added: 'As time has gone by, the information that we are receiving about the terms and conditions of that separation are quite unlike the terms and conditions that were spoken of so loosely during the 2016 campaign'.
Commenting on the cross-party nature of the grassroots movement, Chuka Umana, MP for Lambeth which had the highest Remain vote in the country, said: "We need more Conservative members of parliament to be as fearless as Anna and many others who defied the whip and put their country before their party".
If the deal is rejected by the British public, Britain would "simply stay" in the EU, Sir Patrick said. "Collectively, we're on the verge of one thing extraordinary".
He said the group does not oppose the result of the 2016 European Union referendum or call for a second referendum.
James McGrory, the executive director of Open Britain, said: "When we have been going around to local communities and talking to people about Brexit, there's a real feeling that people are being shut out of a debate in London and Westminster".