Justin is a Fianna Fáil Councillor and a member of Dun Laoghaire–Rathdown County Council.
Justin lives in Dalkey with his wife and three children. He contested the 2019 local elections and was co-opted to replace Cormac Devlin TD on his election to Dáil Éireann in February 2020.
Justin is the Councillor for the Dún Laoghaire Local Electoral Area (LEA) on Dún Laoghaire-Rathdown County Council.
As a Councillor he represents the following areas: Clonkeen, Dalkey, Deansgrange, Dún Laoghaire Town, Killiney, Glasthule, Glenageary, Johnstown, Monkstown, Mounttown, Sallynoggin, Salthill, Sandycove, Seapoint & Stradbrook (Blackrock).