People Before Profit has announced that former TD Gino Kenny has been selected to replace Darragh Adelaide on South Dublin County Council following Mr Adelaide's resignation.
Mr Adelaide was elected in the local elections in 2024 and represented the Clondalkin electoral area.
His resignation was due to personal reasons, the party said.
The party confirmed that Mr Kenny, who failed to be re-elected at the last general election in Dublin Mid-West, has accepted a nomination to replace Mr Adelaide.
He is due to take up the position in April.
During his time as a councillor, Mr Adelaide campaigned on issues such as local bus cancellations and the war in Gaza while also being a prominent figure in the campaign against racism in Ireland.
He also canvassed for President Catherine Connolly during her presidential election campaign.
In a statement, People Before Profit said Mr Adelaide has been an "exemplary councillor".
"He has represented and fought for his constituents and for working class people across SDCC.
"He has also played a central role in standing up to racism and the far right and building a vibrant antiracist movement in Dublin and beyond," the party said.
Mr Kenny also paid tribute to Mr Adelaide, describing him as a "dynamic" activist.
"It's disappointing that Darragh is stepping down, but we fully respect his decision. It was an honour to be a councillor and TD for 16 years until the general election in 2024.
"This certainly wasn’t in the plans, but again it will be a privilege to represent People Before Profit in the Clondalkin LEA," Mr Kenny said.
