The fate of Sydney's last two Lady-class ferries has been sealed, after about four decades plying the city's harbour.

Despite a campaign by locals and a petition, the Lady Northcott made her final regular service on Tuesday from Manly to Circular Quay, before sailing under the Harbour Bridge at about 1pm to be tied up at the Balmain Shipyard.

The other Lady-class ferry, the Herron, was berthed at the shipyard a week ago, marking the end of an era for crews and passengers alike.

Transport for NSW confirmed that both Lady-class ferries had completed their "final regular services" and would now be retired, following the entry into service of five of Sydney's six new Emerald-class ferries built in Hobart.