Sinn Fein and SDLP MPs have been in Dublin for the first meeting of the parliamentary committee reviewing the workings of the Good Friday Agreement.
The four were joined by TDs and senators from the Republic
Northern Ireland's 18 MPs were allowed to attend committee meetings in the Irish parliament from Thursday.
The privilege was used by nationalists but unionists declined the invitation.
MPs will not be allowed to vote in the Dail, but can attend meetings such as the new committee on the Implementation of the Good Friday Agreement.
Alasdair McDonnell and Eddie McGrady from the SDLP and Sinn Fein's Pat Doherty and Michelle Gildernew attended the committee meeting.
The four were joined by TDs and senators from the Republic in their work reviewing how the Good Friday Agreement is being implemented.
The Northern Ireland MPs can take part in the committee's debates but will not have a right to vote or to move motions and amendments.
Speaking after the meeting, Mr McDonnell said he could understand unionist concerns and discomfort in relation to the initiative.
"I think we've got to move on and find structures which they can co-operate with," said the SDLP deputy leader.
"We've got to ensure that what we do accommodates and facilitates the unionist interest."
The meeting was held in a Dail committee room (Picture courtesy of the Houses of the Oireachtas)
Northern Ireland Agricultural Minister Michelle Gildernew said the committee was the first step in achieving full representation for NI politicians in the Dail.
"We would like to see further work ongoing in Dublin to give us and our constituents in particular the right to be represented in our national parliament," she said.
"This is an important first step but it is only a first step and I think there does really need to be a lot more work on going here in Dublin on getting proper representation for the people of Fermanagh/south Tyrone and other constituencies."
Committee chair, Fianna Fail deputy Noel Treacy, described the meeting as "an historic occasion".
"This is a truly historic day and one that is unprecedented in the history of our parliament," he said.
Fine Gael's Cavan-Monaghan TD Seymour Crawford said it was a major step forward in north-south relations.
"It is a major breakthrough that we are all able to sit around the one table here in Dail Eireann," he said.