The ferries will be used on sailings between Lochmaddy, Uig and Tarbert on the Isle of Harris.
Both vessels will be built at Cemre Marin Endustri A.S shipyard in Turkey, with expected delivery dates of June and October 2025 respectively.
They will be built to the same specification as the vessels to be used for Islay, which are already under construction in Turkey.
Jim Anderson, director of vessels at CMAL said: “We have been encouraged by the timescales the yard is achieving with the Islay vessels, with the most recent milestones being reached three weeks ahead of schedule.
"These new ferries will deliver dedicated services during peak seasons to Lochmaddy and Tarbert, increasing capacity and resilience to the Outer Hebrides.”
It comes at a time when at least half of the vessels in CalMac's fleet are over 25 years old, while since 2007 only five new ferries have been delivered to the ferry operator.
Minister for Transport Jenny Gilruth said: "I’m pleased the final details of the contract for these additional vessels are now in place to allow work to get under way in earnest. The update on delivery timescales falling within 2025 for these additional vessels is very welcome."
Ms Gilruth added: "Our intention is that these additional vessels will be deployed on the Little Minch routes, delivering dedicated services to communities in the peak season rather than the shared vessel operation currently in place. This will create the opportunity for significantly increased capacity and resilience for the communities of the Western Isles.
Councillor Uisdean Robertson, from Comhairle nan Eilean Siar said: "CMAL and Scottish Government have acted decisively in ordering these two new ferries dedicated to the services between the mainland and Uist and Harris.
"It is extremely welcome to receive good news on the future of our lifeline ferry services to the Outer Hebrides following the constrained capacity on Little Minch routes. We can look forward with confidence in the build timescale to a future where our economy is not held back by ferry services.”
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