Fine Gael's Declan Doocey was proposed by his party colleague Damien Geoghegan and seconded by Fianna Fáil's James Tobin.
Current and former senators, the bishop of Waterford and Lismore as well as Councillor Doocey's family members gathered to pack out City Hall for thre occasion.
Councillor Doocey, from Lismore, won out over Sinn Féin's Pat Fizgerald, besting him by 20 votes to 7.
Fianna Fáil's John O'Leary was elected unopposed as Deputy Mayor.