His first spaceflight was a long-duration mission to the International Space Station as a flight engineer on the Expedition 19 and 20 crew.

In 1991, Barratt completed both a residency and a Master of Science in aerospace medicine jointly run by Wright State University, NASA, and Wright-Patterson Air Force Base.

He spent over 12 months working and training in the Gagarin Cosmonaut Training Center in Star City, Russia as one of two flight surgeons supporting Norman Thagard and his backup Bonnie Dunbar, a role that often included negotiations to resolve different approaches to medicine by NASA and Russian doctors.

Barratt served as lead crew surgeon for ISS Expedition 1 from July 1998 until selected as an astronaut candidate.

Following the completion of two years of training and evaluation, he was assigned technical duties in the Astronaut Office Station Operations Branch.

During NEEMO 7 the crew tested technologies and procedures for remote surgery, as well as using virtual reality for telemedicine.

[5][6] Barratt was assigned to the Expedition 19 crew in February 2008[7] and launched to the International Space Station in March 2009 aboard Soyuz TMA-14.

The shuttle also carried the third of four ExPRESS Logistics Carriers to the ISS, as well as a humanoid robot called Robonaut.

He is married to Dr. Michelle Lynne Barratt (née Sasynuik); they reside in League City, Texas, and have five children.

His personal and recreational interests include family and church activities, writing, sailing,[18] and boat restoration and maintenance.