Liadh Ni Riada will contest the presidential election as the Sinn Féin candidate.
Ms Ni Riada was selected at a meeting of the party’s Ard Comhairle on Sunday afternoon.
She is the party’s MEP for Ireland South and a former television producer.
She joins four other candidates who will be on the ballot paper on polling day next month.
Sitting president Michael D Higgins can nominate himself and plans to seek a second term in office.
Meanwhile, three other candidates have secured the backing of four local authorities to lodge nomination papers.
Businessman and 2011 runner-up Sean Gallagher, his former Dragon Den co-star Gavin Duffy and Senator and Pieta House founder Joan Freeman have received four local authority nominations apiece.
A Red C poll, reported in the Sunday Business Post today, puts Michael D Higgins at 67pc – with the next most popular candidate, Sean Gallagher, trailing at 15pc.