Meir earned degrees from Brown University, International Space University, and Scripps Institution of Oceanography, then worked in human physiology research tied to NASA's shuttle and station programs. Her pre-astronaut work included reduced-gravity flights, NEEMO underwater analog operations, Antarctic and Belize diving expeditions — open definition, and a faculty position at Harvard Medical School and Massachusetts General Hospital.

NASA selected Meir in Astronaut Group 21 in 2013. Before her first launch, she built operational experience as a Capsule — open definition Communicator, supported ISS spacewalks — open definition from Mission Control — open definition, trained in station systems and robotics, and completed analog work through ESA CAVES and NASA Desert RATS.

Her first spaceflight launched on Soyuz MS-15 in September 2019 and kept her aboard the International Space Station — open definition through Expeditions 61 and 62. She served as a flight engineer — open definition, contributed to hundreds of investigations, completed the first three all-woman spacewalks with Christina Koch, and logged 205 days in space across 3,280 Earth orbits.

In February 2026, Meir commanded NASA's SpaceX Crew-12 mission aboard Crew Dragon Freedom with Jack Hathaway, Sophie Adenot, and Andrey Fedyaev. Crew-12 restored and sustained station staffing during Expeditions 74 and 75, making Meir a rare astronaut whose record combines scientific field research, historic EVA work, Soyuz operations, and Commercial Crew — open definition command.