Former Fine Gael MEP Mr Chris O'Malley is to replace the Labour TD, Mr Eamon Gilmore, on Dún Laoghaire-Rathdown County Council.
Mr Gilmore has stood down in line with the party's support for the ending of the dual mandate whereby members of the Oireachtas can no longer be members of local authorities. The legislation giving effect to the measure is expected to be passed by the Dáil early next month.
Mr O'Malley, a grandson of Kevin O'Higgins, joined Labour nine years ago , when, he said, it had become clear to him the party was the most determined of the major parties in pursuing the social-democratic objectives he believed in.
He was Mr Gilmore's director of elections in the last general election and was chosen at a convention to replace the TD.
In the last local elections, Mr Gilmore topped the poll in the Dún Laoghaire ward with 2,490 first-preference votes.
Meanwhile, Independent councillor Mr Vincent McDowell has joined the Labour Party, bringing to seven the number it has on Dún Laoghaire-Rathdown County Council.
He said he would be asking his supporters in Dún Laoghaire to vote for Labour candidates in next year's local elections.
