Ms Whitson - hailed as an "American space ninja" - has spent 665 days in space over three missions
Record-breaking astronaut Peggy Whitson has returned to Earth along with two of her fellow International Space Station crew members.
Whitson, her NASA colleague Jack Fischer and Russia's Fyodor Yurchikhin landed in Kazakhstan at around 2.30am Irish time.
Ms Whitson - who has served as ISS commander twice - broke the US record for cumulative time in space back in April, and has now spent a total of 665 days in space over the course of three missions (over 130 days more than previous record holder Jeff Williams).
Seven Russian men have logged more time in orbit - including Gennady Padalka, the world record-holder with 878 days.
Ms Whitson's latest stint in space lasted 288 days, having arrived on the ISS last November.
She also holds multiple other records - including more time in orbit during a single flight than any other woman, and most spacewalks (10) by a female astronaut.
638 days in space and the view is still amazing! Soaking up some sunset time in the cupola… pic.twitter.com/AiReQzkjJZ— Peggy Whitson (@AstroPeggy) August 6, 2017
NASA says Whitson and Fischer "contributed to hundreds of experiments in biology, biotechnology, physical science and Earth science" during their time in space.
Specific experiments included a lung tissue study, and an examination of the physical changes to astronauts' eyes in microgravity.
The station's latest commander Randy Bresnik hailed Ms Whitson as an "American space ninja".
He told the departing crew members: "We are in your debt for the supreme dedication that you guys have to the human mission of exploration."
Additional reporting by IRN