A convincing win in a "unique" by-election has been welcomed as an invitation to work harder by one state premier, as it adds pressure on his political opponent.

Former journalist Katelin McInerney won the NSW South Coast seat of Kiama for Labor at a weekend by-election with 60 per cent of the vote.

It bolsters the minority Labor government's position while adding to pressure on Opposition Leader Mark Speakman.

Premier Chris Minns said the circumstances of the by-election were "pretty unique".

"The incumbent member's sitting in jail," he told ABC Radio Sydney on Monday.

Gareth Ward's 14-year hold on Kiama ended in August when he resigned as parliament was preparing to expel him.

His legal bid to hold the seat after being convicted of sexual and indecent assaults failed.

Ward first w

See Full Page