The ships, MSC's seventh and eighth World-class vessels, will be built by France's Chantiers de l'Atlantique shipyard. Construction will get under way in 2029.
The deal, which is subject to access to financing, extends the value of MSC's current orders with the firm this year to nearly €7 billion, with Chantiers currently working on another two World-class ships.
MSC announced the order at a joint event this week celebrating the float out of MSC World Asia and MSC World Atlantic's coin ceremony.
World Asia will join the MSC fleet in 2026 followed by World Atlantic in 2027. World-class vessels five, six, seven and eight are yet to be named.
All of MSC's World-class vessels feature dual-fuel liquefied natural gas (LNG) engines, which can utilise bio and synthetic fuels.
Pierfrancesco Vago, executive chair of MSC Group's cruise division, said the line was seeking to "set new standards for the future of cruising" with its World-class fleet.
"These are some of the most energy efficient ships in the world," he claimed, adding: "We continue our commitment to LNG, ensuring we are ready for future renewable fuels.
MSC World Asia is due to be delivered in November 2026 and will, from December, begin sailing seven-night itineraries in the western Med calling in Barcelona, Marseille, Genoa, Civitavecchia (for Rome), Messina and Valletta.
MSC World Atlantic, meanwhile, will enter service in 2027 and will be deployed in the Caribbean Sea and will sail from Port Canaveral during the 2027/28 winter season.
