The EU's chief Brexit negotiator Michel Barnier has warned that the UK leaving the EU changes the union's border - but he insisted he will work "to avoid a hard border".
Mr Barnier - who has previously served as a European Commissioner and held various French cabinet positions - will hold a private meeting with Enda Kenny after the special joint sitting at Leinster House.
He has already been in Dublin, seven months ago during a tour of European capitals.
This two-day trip will include a visit to the North and the border region, with the aim of getting a clearer vision of just how Brexit will affect Ireland.
Today Mr Barnier is south of the border, where he enjoyed a rare honour in Leinster House - making a speech to a joint sitting of the Dáil and Seanad.
Such an opportunity has previously been afforded to the likes of Nelson Mandela, Bill Clinton and Tony Blair.
Mr Barnier told the gathered politicians: "Ireland is stronger in the union, and the EU is stronger with Ireland.
"I want to reassure the Irish people, in this negotiation Irish interests will be the union's interests."
He stressed that the Irish border will be one of his three priorities in the first phase of negotiations with the UK.
He noted: "If the conditions are right, a close partnership with the UK is in everybody's interest - and in Ireland's interest in particular."
He called for talks to take place with 'mutual respect' and 'without aggressivity', arguing: "If we are open to finding solutions, there is no reason why a strong Europe cannot maintain a strong relationship with the UK."
"Message of hope and determination"
The veteran French politician assured TDs and senators that he would work to avoid a hard border despite the unavoidable changes to the existing EU border.
He warned that there would be consequences from Brexit, including to the remaining EU member states - but he insisted that nothing in the process should put the peace process at risk.
"I want to listen to the concerns of the Irish people, but I also want to pass on a message of hope and determination," he stressed, saying he is determined to reach a deal with the UK.
Mr Barnier cited a number of benefits of EU membership, saying: "Irish airlines have been the first to take advantage of [EU airspace] benefits, and have profoundly changed the market.
"I experienced it firsthand myself when I flew to Dublin yesterday night, on a well-known low-cost carrier. Still no coffee, but a little bit more seat space than before."
Mr Barnier will this afternoon hold a private meeting with the Taoiseach in Government Buildings.
Meanwhile, business group IBEC met with Mr Barnier earlier this morning.
CEO Danny McCoy said: "There is a welcome recognition in Brussels of the unique risks Brexit presents to Ireland. These now need to be directly and explicitly addressed in negotiations and in the terms of a future EU-UK trade deal.
"Tailored Irish provisions will need to cover free movement of people, but also the massive trade exposure of key sectors and the potential impact on highly integrated cross-border supply chains."
