The American astronaut, 52, has posted stunning photos of sunrises and sunsets during his year in orbit.
This is Kelly's fourth mission, bringing his career total to 520 days in space. He'll hitch a ride back to Earth tonight on Russia's Soyuz spacecraft, arriving around 11:25 p.m. ET in Kazakhstan.
Once he's back on Earth, NASA will put Kelly through a series of tests to understand how his body coped with the stress of living in space. Those results will be compared to his identical twin brother, retired astronaut Mark Kelly, who remained on Earth.
The results could yield new insights for NASA as it prepares to one day send a crew on a mission to Mars.