Pettit worked as a scientist at the Los Alamos National Laboratory from 1984 until 1996, when NASA selected him as an astronaut candidate.

He was a junior advisor to the Synthesis Committee of the Space Exploration Initiative on its May 1991 report "America at the Threshold", recommending plans for a human mission to Mars.

[3]: A-7 An astrophotographer, Pettit captured thousands of unique star trails and photographic data sets, which he regularly shares online.

During his six-month stay aboard the space station, he performed two EVAs to help install external scientific equipment.

During free time on his stay aboard the International Space Station, he conducted demonstrations showing how fluids react in an extremely low gravity environment in a series he called "Saturday Morning Science".

[7][8] Pettit was left exhausted and reportedly dislocated a shoulder, but the space agencies downplayed the situation saying the astronauts were in good shape.

This presents a plausible mechanism for the initial stages of planetary formation, since particles of this size do not have sufficient gravity to cause this phenomenon.

The Dragon capsule was carrying supplies for the ISS, and the successful capture demonstrated the feasibility of using privately developed spacecraft to resupply the station.

[19][20] During Expedition 6, Pettit used spare parts found throughout the Station to construct a barn door tracker; the device compensates for the movement of the ISS relative to the Earth's surface, permitting sharper high resolution images of city lights at night from the orbiting space station.

[21][22] In November 2008, Pettit invented the zero-g coffee cup, which used the wetting angle to carry fluid along a crease to permit drinking and avoid the necessity of a straw.