Orbiting above the Himalayas, Kelly tweeted "records are meant to be broken." It was his 383rd day living in space during four missions, according to NASA.
Kelly is now more than halfway through a nearly year-long mission aboard the International Space Station.
The one-year mission is a chance for scientists to study how the human body responds to long-duration space flights, NASA says. On Earth, scientists are performing parallel studies on Kelly's identical twin brother, retired astronaut Mark Kelly.
Scott Kelly took the American longest-cumulative-time-in-space title from astronaut Mike Fincke, according to NASA.
"Breaking such a record for time in space is important because every additional day helps us better understand how long-duration spaceflight affects bodies and minds, which is critical to advancing NASA's journey to Mars," NASA said in a press release on Friday.
Kelly is scheduled to come down to Earth on March 3, according to NASA, after having totaled 522 days in space. He launched on March 27 from Kazakhstan aboard a Russian Soyuz rocket along with two cosmonauts. One of the cosmonauts, Mikhail Kornienko, will also stay up for the one-year mission.
Another Russian cosmonaut, Gennady Padalka, owns the world record for most days spent in orbit. He returned to Earth on September 12 with a cumulative total of 878 days in space, according to Russia's Federal Space Agency.
Aboard the space station and at a speed of about 15,500 miles per hour, Scott Kelly is hurtling towards another record -- the single-longest space flight by an American. He'll hit that mark on October 29, NASA says. That will be Kelly's 216th consecutive day in space.