| Name | Position | Party | Constituency |
|---|---|---|---|
| Joe O'Brien | TD | Green Party | Dublin Fingal |
| Eoghan O'Brien | Councillor | Fianna Fáil | Howth-Malahide |
| Terry O'Brien | Councillor | Labour | Tralee |
| Darragh O'Brien | TD | Fianna Fáil | Dublin Fingal |
| Clare O'Byrne | Councillor | Green Party | Firhouse - Bohernabreena |
| Jim O'Callaghan | TD | Fianna Fáil | Dublin Bay South |
| Denis O'Callaghan | Councillor | Labour | Killiney-Shankill |
| Cian O'Callaghan | TD | Social Democrats | Dublin Bay North |
| Alan O'Callaghan | Councillor | Fianna Fáil | Killaloe |
| Sheila O'Callaghan | Councillor | Fianna Fáil | Cobh |
| Bobby O'Connell | Councillor | Fine Gael | Castleisland |
| Guss O'Connell | Councillor | Independent | Palmerstown - Fonthill |
| Ross O'Connell | Councillor | Social Democrats | West Cork |
| Sean O'Connor | Councillor | Unknown | Cobh |
| Alan O'Connor | Councillor | Green Party | Cobh |
| Oisín O'Connor | Councillor | Green Party | Glencullen-Sandyford |
| James O'Connor | TD | Fianna Fáil | Cork East |
| Gerry O'Connor | Councillor | Fine Gael | Ratoath |
| Claire O'Connor | Councillor | Fianna Fáil | Pembroke |
| Charlie O'Connor | Councillor | Fianna Fáil | Tallaght Central |
| Martina O'Connor | Councillor | Green Party | Galway City Central |