In Fiume, initially, he lived as a landlord and commercial agent for his brother Lorenzo, who ran a trading company in Livorno, but Giovanni de Ciotta soon turned to engineering.
Hungarian support proved to be crucial to the development of the port of Fiume and Ciotta was the key person in assuring it.
[4] Under his leadership an impressive phase of expansion of the city began, marked by the completion of the railway from Fiume to Budapest, the construction of the modern port, and the initiation of modern industrial and commercial enterprises such as the Royal Hungarian Sea Navigation Company "Adria", and the Whitehead Torpedo Works, where his contribution was crucial as he financed Robert Whitehead's efforts in producing a viable torpedo.
The “Ciotta system” underwent a crisis in 1896 when Hungarian Prime Minister Dezső Bánffy began a centralizing policy towards Fiume.
Ciotta, being unable to assure the equilibrium between Fiume and Hungary, resigned and retired to private life, following the Governor Lajos gróf Batthyány de Nemetujvár.