The two identical ships will be built by Fincantieri - the largest the Italian shipyard has ever built.
They are due for delivery in 2024 and 2026 respectively.
The order will bring Tui Cruises’ Mein Schiff fleet up to nine ships by 2026.
It is the latest step in the line’s “sustainable growth” strategy as part of its joint venture with Royal Caribbean Cruises Ltd.
