A Fianna Fail senator who compiled the first Irish parliamentary report on a united Ireland has criticised calls for a border poll at the Beyond Brexit weekend event in Belfast.
More than 1,500 people attended the Waterfront Hall event, which examined the future of Northern Ireland and the Republic after the UK leaves the EU.
The event was organised by Ireland's Future, a collective of Irish citizens living here and seeking to highlight the potential impact of Brexit on their rights and livelihoods.
During her speech Sinn Fein leader Mary Lou McDonald called for the Irish Government to convene a forum to begin planning for reunification.
Senator Mark Daly said the idea of holding a border poll in the near future would be "foolhardy".
"The lesson of Brexit is that you do not hold a border poll without having long-term engagement and knowing all the facts," he said. "The idea of having a referendum on a united Ireland without serious and long-term engagement would be a recipe for disaster.
"The referendum was held without any facts about what leaving the EU would mean. So it would be foolhardy to follow that up with the border poll. That's not helpful.
"A border poll would be a colossal undertaking. No one in government in the south is looking at the practicalities of a border poll. There is no plan."
The Kerry senator compiled his report in 2017 for a Seanad committee tasked with looking at the impact of Brexit on the Republic, which also set out proposals for peaceful reunification.
Ms McDonald told the conference that crashing out of the EU with no deal in place would lead to a hardening of the border.
"A hardening of the border is inconceivable and will be met with the demand for a unity referendum," she said.
"We don't exactly know what will happen over the next few weeks or months. It's not in our hands, it's in the hands of a minority Tory Government in London, and that is the crux of the problem.
"It's irresponsible and arrogant for a Dublin Government to shout down any prospect of a unity referendum."
While there were no unionist politicians speaking at the event, Ms McDonald issued a direct message to the unionist community saying they would "have a home in a united Ireland".
SDLP leader Colum Eastwood, however, said now was not the right time for a border poll.
"There are unionists who are willing to engage and explore new possibilities," he said.
"Unionism should have nothing to fear in a conversation based on persuasion and consent. My appeal to unionism is this: try to convince us of your vision for the future and we'll try to convince you of ours, and then in time let the people decide."