Former Belfast mayor Niall Ó Donnghaile is stepping down from the Seanad due to poor health.
The one-time Sinn Féin press officer, who previously represented the Pottinger district on Belfast City Council, has been a senator since 2016.
The 38-year-old said he had been unable to attend the Oireachtas since the summer recess on the advice of his doctor.
“It is unlikely that this situation will change in the short-term, therefore, I feel the best decision for myself, my family and the party going forward is to resign from the Seanad and step back from public life,” he said.
“It has been a great pleasure over the course of many years to first of all serve the people of the Short Strand as a councillor, the people of Belfast as mayor and latterly giving a voice to those in the north in the Seanad. But the time is now right for me to step aside from this public role.”
Sinn Féin leader Mary Lou McDonald thanked Mr Ó Donnghaile for his contribution to the Seaned over the past eight years and expressed hope that he “can overcome the health challenges that he has had to deal with over the past number of months”.
“Niall served diligently during that period, and indeed prior during his time as a member of Belfast City Council and as ardmhéara Beál Feirste,” she said.
“In particular, Niall made a valuable contribution to the Joint Oireachtas Committee on the Implementation of the Good Friday Agreement.”
Ó Donnghaile became Belfast’s youngest lord mayor a matter of weeks after being elected a councillor in 2011, aged 25.