Kenya Airways will introduce two Boeing 777-300ER aircraft in October 2013 and May 2014 following an agreement with lessor GECAS.
The twinjets will join the fleet to serve such routes as Amsterdam, Bangkok, Guangzhou and Dubai, said the carrier.
Kenya Airways has signed an operating lease for the aircraft which runs to 12 years. The jets will be fitted with around 400 seats, some 78 more than the carrier's 777-200ERs.
It follows a letter of intent for two 777-300ERs sealed earlier this year, when the carrier indicated the jets would arrive at the end of 2012 or in early 2013.
Chief executive Titus Naikuni said the larger aircraft would "significantly increase" the airline's passenger and freight capacity, and bring lower costs, while improving its premium service product to Europe and the Asia-Pacific region.