Oleg Kononenko and Nikolai Chub spent 374 days in low-Earth orbit at the ISS, the longest time anybody has ever stayed on the station in a continuous stint.
During his stay, Kononenko, 60, also set a new record for the longest cumulative time any person has spent in space -- passing the three-year mark with a total of 1,111 days across five trips.
American astronaut Tracy Dyson, who took off for the station in March, also returned to Earth.
The Soyuz MS-25 capsule carrying the three landed in the vast steppe of Kazakhstan at 16:59 local time (1159 GMT), an official broadcast of the landing showed.
The absolute record for the longest unbroken time any human has spent in space belongs to Russia's Valeri Polyakov, who spent 438 days on the Mir space station in 1994-95.
Russia has vowed to quit the ISS, which it says has outlived its purpose, and is planning to launch its own independent space station, though those plans have been beset by delays.
Russia's Roscosmos state space agency is seeking new partnerships with countries in Asia, Africa and the Middle East.
In a rare form of cooperation between Washington and Moscow amid tensions over Ukraine, US and Russian astronauts jointly stay aboard the ISS and Russian Soyuz craft ferry them to and from the station.
The ISS spans the size of a football field and orbits some 250 miles (400 kilometres) above the Earth.
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