Delegates from the EPP are meeting in Wicklow, south of Dublin, and Mr Barnier is expected to address their session on Friday after being given a tour of the border by Charlie Flanagan, the Irish foreign minister.
"I will work with you to avoid a hard border".
Ireland is anxious that Brexit could prove hugely disruptive to its economy due to its strong trade links with Britain.
This refers to the significant amount of trade that the Republic of Ireland has with the United Kingdom, the exposure of the Irish economy to United Kingdom trade and Brexit and the land border with Northern Ireland.
Mr Barnier further outlined that protecting Ireland's interests would be an important part of the Brexit negotiations.
At Fitzpatrick's pub, between Carlingford and Dundalk, people said they would welcome a visit from the man who will negotiate on the EU's behalf. To the alarm of Unionists, the formal European Union position is very clear: in view of the unique circumstances on the island of Ireland, flexible and imaginative solutions will be required, including the aim of avoiding a hard border.
Malaysia, North Korea Asian Cup qualifier to go ahead in Pyongyang
He was accused of stealing a propaganda poster, and North Korean officials released a video that purported to show him taking it. Earlier this month, American colleague Kim Sang-duk, who is also known as Tony Kim, was arrested on similar charges.
Nearly twice as much time has been set aside for TDs to speak as has been allocated to Mr Barnier. Ireland is widely considered the European Union member with the most to lose when the Brexit materialises. Dublin is seen as a popular choice, with large corporates such as JPMorgan seeking to set up shop there.
Barnier stressed: "I want us to reach a deal".
Official Brexit negotiations will start following a general election in Britain on June 8. "Nothing in this negotiation should put peace at risk".
Barnier is visiting Ireland in order to gauge the potential impact of Brexit on the UK's closest neighbour, and added that he was hopeful the negotiations will produce an end result both sides will be content with.
He repeated the EU's position that the issue of the UK-Ireland border, citizens' rights and "the financial settlement" must be the first priorities for talks.
One of the party's MEPs, Matt Carthy, said: "People in the North are entitled, under worldwide law, as a result of the Good Friday agreement, to Irish citizenship".