The former deputy speaker of the Northern Ireland Assembly is to stand in the European elections if they take place in Northern Ireland.
Jane Morrice, the Women’s Coalition founder and peacemaking expert, said it was her duty to speak out against the “harmful” effects of the UK’s withdrawal from the EU.
The UK has begun making preparations to hold a poll next month, but will cancel the elections if Brexit happens before then.
Ms Morrice said: “If the elections to the European Parliament give me the opportunity to find ways to reduce the harm of Brexit on Northern Ireland, I must stand up and be counted.”
She describes herself as a “dedicated and devoted European”, and would enter the race as an independent candidate.
She added: “Brexit is bad for Northern Ireland.
“It threatens the political, economic and social fabric of our society and could serve to halt, even reverse, our hard-won peace process.
“As an elected member of the European Parliament, standing as an independent, I will do everything in my power to ensure that does not happen.”
She was one of the architects of the first multimillion-pound EU Peace Programme in Northern Ireland, in her role as head of the European Commission office in Belfast.
She has campaigned to keep EU funding for peace in Northern Ireland.
Ms Morrice added: “With increasing calls for independence in Scotland and a border poll in Ireland, Brexit is not only bad for economic, social and political progress in Northern Ireland.
“It also threatens the break up of the United Kingdom.
“Those who back Brexit must recognise this risk and find ways to reduce its negative impact by supporting my proposal to keep Northern Ireland in the EU as part of the UK – and putting the new deal to the people, with an option for the UK to remain.”
After the Brexit referendum, she launched a petition calling for Northern Ireland to be given honorary EU association as a European place of global peace-building.
It has attracted 6,500 signatures.
She backed calls for a second referendum.
She said any deal “must contain a safety net for Northern Ireland which will secure our economic progress and prosperity by giving us the best of both worlds and, above all, protect our precious peace process”.
She said her track record in politics, working within the Women’s Coalition on the fringes of the Good Friday Agreement negotiations and as deputy speaker of the first Stormont Assembly, was proof of her determination to make Northern Ireland a better place for everyone.