NASA's Scott Kelly and Roscosmos' Mikhail Kornienko will take part in the mission set to start in spring 2015. The space agencies said in a statement Monday that the flight would help reduce health risks for planned NASA missions around the moon, an asteroid and ultimately Mars.
Crews so far have done only six-month stints on the station.
William Gerstenmaier, NASA's associate administrator, said the mission "will increase our knowledge regarding the effects of microgravity on humans as we prepare for future missions beyond low-Earth orbit."
Kelly and Kornienko will start training for the mission next year.