The Carnival Cruise Line fleet has reached 27 ships with the addition of Costa Firenze from sister line Costa Cruises.
Built in 2021, the ship can carry as many as 5,260 passengers.
The vessel was handed over in Cadiz, Spain, ahead of a two month refurbishment project.
The renamed Carnival Firenze is due begin sailing year-round from Long Beach in California on April 25.
Three and four-day sailings to Mexico and Catalina Island will be combined with five to seven-day itineraries to the Mexican Riviera, visiting Cabo San Lucas, Mazatlan and Puerto Vallarta.
The vessel is the second to join the US fleet from Italian line Costa following the transfer of Costa Venezia, originally designed for the Asian market, last year to operate from New York as Carnival Venezia.
Both ships feature Italian touches, with Carnival Firenze’s atrium modelled after Florence’s main public square, Piazza del Duomo, while the lido deck draws inspiration from the Italian Riviera.
The ship will feature many Italian-themed food and drink options popular on Carnival Venezia.
Carnival Cruise Line president Christine Duffy said: “The beauty of Florence, Italy is about to meet the fun of Carnival Cruise Line.
“We are elated to welcome Carnival Firenze to the Carnival fleet, joining her sister Carnival Venezia to showcase Carnival Fun Italian style.”