Cross-party pact elects O'Sullivan as mayor of new council
She was elected as mayor of the Waterford city Metropolitan District by 11 votes for, with five against in the newly-amalgamated, 32-seater council.
Independent councillors Sean Reinhardt and Joe Kelly abstained from the vote.
A married mother-of-four in her 40s, Mrs O'Sullivan defeated the Independent councillor Mary Roche, a former mayor of Waterford city who is a married mother and grandmother.
Sinn Fein's Pat Fitzgerald seconded the motion. Mrs Carey's nomination was unopposed.
Mrs O'Sullivan said she was "honoured and humbled to represent our great city" as the first Mayor of the city and county in the metropolitan area.
She was mindful of the workers at Bausch + Lomb, who are at threat from 200 job cuts, along with a 20pc drop in pay for the remainder.
His party colleague, Jason Murphy, elected for the first time last month, was nominated as Leas Cathaoirleach.