MV Hallaig was built at the town's Ferguson yard and is the first commercial vessel to be produced on the Lower Clyde for more than five years.
It's also the first sea- going vessel of its kind. The project has protected 75 existing jobs and created an extra 100 at the Inverclyde yard.
The unique vessel will go into service in the summer, carrying passengers and vehicles between the Scottish islands of Skye and Raasay.
A second vessel is under construction and will begin operating late next year between Portavadie and Tarbert on Loch Fyne.
The £20 million ferry deal was welcomed by Deputy First Minister Nicola Sturgeon.
She launched the ferry yesterday to the cheers of shipyard workers and guests.
Ms Sturgeon said: "Our £20m investment provided the support needed to produce here on the banks of the Clyde, the world's first seagoing passenger and vehicle roll-on roll-off ferries to use a low-carbon hybrid system of diesel electric and battery power."
The revolutionary ship was named after a poem by the late Raasay-born writer Sorley MacLean. His poem was named after a deserted township on the island.
The ships will be operated by CalMac out of ports owned by Caledonian Maritime Assets.
The firm's chairman, Grenville Johnston, said: "The two new ferries' technology will be cleaner, quieter and cheaper to operate and maintain than ever before."
Yard boss Richard Deane said: "This is a fantastic day – it is great to be back building ships on the Clyde.
"Employment has more than doubled at the yard and we have started to train apprentices again."