The leaders of Sinn Féin will be speaking at the Plaid Cymru's annual conference in Swansea (4-5 October).
Sinn Féin leader Mary Lou McDonald TD will be addressing conference and Michelle O'Neill MLA, Leader in the Northern Ireland Assembly, will be taking part in a panel discussion.
Plaid Cymru leader Adam Price AM said both parties shared a "common vision of our respective nations playing a central role in Europe's future."
Mr Price has invited all pro-Remain parties in Ireland to attend the conference.
The SNP's Alyn Smith MEP, President of the European Free Alliance group and First Vice-President of the Greens/EFA Group in the European Parliament, will also be a speaking guest at the conference.
Plaid Cymru leader Adam Price AM said:
"As the UK government pursues its policy of a hard Brexit that will devastate our economies and communities, it is imperative that the alliance between the parties of Remain is stronger than ever before.
"Because of the sacrifice of people on both sides, it is crucial that the peace process and the Good Friday Agreement is protected.
"Wales and Ireland have a very strong historical bond and I look forward to working with all pro-Remain parties in Northern Ireland as we try to avoid a disastrous crash out Brexit."
Speaking ahead of her conference address, Mary Lou McDonald TD said:
"I look forward to addressing the conference and meeting the delegates. Brexit represents a fundamental challenge to our economy, our agreements and rights of citizens.
"It has the potential to undermine the progress that we have achieved since the signing of the Good Friday Agreement. It is important that all of those who oppose Brexit stand together in the common cause."