Independent TD Catherine Connolly will launch her presidential election bid next week.
The Galway TD is expected to drum up enough support in the Oireachtas to secure a nomination for election, which is due to take place later this year.
To get a name on the ballot paper any prospective candidate needs the support of 20 Oireachtas members.
The National Executive of the Social Democrats unanimously decided on Thursday that its Oireachtas members would back Ms Connolly for president.
Ms Connolly is also expected to secure the backing of People Before Profit as well as several independent TDs and senators.
Sinn Fein and the Labour party have yet to indicate whether they will support Ms Connolly.
The Social Democrats said their decision reflects the strong support throughout the Social Democrats for nominating Catherine Connolly.
“Catherine has been a tireless advocate for progressive causes and we believe she would make an excellent president,” the party said.
Speaking to the Galway City Tribune newspaper, Ms Connolly said her “mind was made up” to run.
“I’ve support from across the spectrum, including the Social Democrats, People Before Profit and Solidarity, as well as a number of senators and others,” she said.
“Labour and Sinn Fein are still completing their own internal processes which I fully respect. I’ll be formally launching my campaign next week.”
Earlier this week, Sinn Fein leader Mary Lou McDonald refused to rule herself out of running to become the next president of Ireland.
It appeared to be a change of position from March, when Ms McDonald said she would not be running, and that she was focusing on work towards a future Sinn Fein government.
In June, Sinn Fein vice president Michelle O’Neill also did not rule herself out from running to succeed current Irish President Michael D Higgins.
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