Speakers are addressing a rally outside Leeds Art gallery on The Headrow.
Founder of Stop Brexit Ltd Peter French said: "I am on the stage now looking out. It is just a sea of people.
"It says to me in a city that is 50/50 there's a lot to play for.
"I wholeheartedly believe we can stop Brexit and this gives me added purpose that we can do that."
Leeds was one of the most divided areas during the 2016 European Referendum with 50.3 per cent voting to remain and 49.7 voting leave.
Speaker AC Grayling said: "I think it is absolutely fantastic. I know Leeds in recent years has not been what you would describe as a radical city.
"It shows Yorkshire and Leeds is waking up to the fact that we have to stop Brexit."
He added: "We know that there's a majority of politicians in both Houses for Remain and what they are watching and waiting for is a continuing change in public opinion to enable them to vote this down."
Chair of Leeds for Europe, Richard Wilson, said politicians needed to take note.
"Labour are an example, after recent events," he said. "They need to listen to ordinary people. We are growing all the time.
"I have been here 20 minutes and people are still passing me.
"I don't think Leeds will have seen a march this big in recent modern history.
"It tells me there's a massive feeling against Brexit in the north of England."