The airline said it had signed an agreement with the US airframer to take the aircraft. It has not disclosed an engine selection.
Transaero said the twinjets would be configured with four first-class, 14 business-class and 244 economy-class seats.
Director general Olga Pleshakova said the airline was "sticking to a principle of innovation" with the decision.
She added that the carrier had already made advance payments to secure the 787s, which will be used to replace Boeing 767s used by the Moscow-based operator.
"This aircraft, which has become a symbol of emerging technology, has the highest efficiency," said Pleshakova.
Transaero has already tentatively signed for Airbus A380 and Boeing 747-8 aircraft, and placed an order for eight Airbus A320neos.