- Matt Damon as Dr. Mark Watney, a botanist and mechanical engineer who is part of the Ares III team.
- Jessica Chastain as Commander Melissa Lewis, USN Submarine Warfare officer, oceanographer, geologist and the Ares III mission commander.
- Kristen Wiig as Annie Montrose, the director of media relations for NASA.
- Jeff Daniels as Theodore "Teddy" Sanders, the Administrator of NASA.
- Michael Peña as Major Rick Martinez, USAF officer, engineer, pilot of the Ares III mission for MAV.
- Sean Bean as Mitch Henderson, the Hermes flight director
- Kate Mara as Beth Johanssen, the Ares III's system operator.
- Sebastian Stan as Dr. Chris Beck, flight surgeon for the Ares III mission.
- Aksel Hennie as Dr. Alex Vogel, a German national who is the navigator and chemist of Ares III.
- Mackenzie Davis as Mindy Park, a satellite planner in Mission Control.
- Benedict Wong as Bruce Ng, director of Jet Propulsion Laboratory (JPL).
- Donald Glover as Rich Purnell, a JPL astrodynamicist.
- Chen Shu as Zhu Tao (Chinese: 朱涛), deputy chief scientist at the China National Space Administration.
- Eddy Ko as Guo Ming (Chinese: 郭明), chief scientist at the China National Space Administration.
- Chiwetel Ejiofor as Vincent Kapoor, NASA's Director of Mars Missions.[6][7]
- Nick Mohammed as Tim Grimes
Chastain prepared for her role by meeting with astronauts and scientists at the Jet Propulsion Laboratory and the Lyndon B. Johnson Space Center. She was inspired by astronaut Tracy Caldwell Dyson, saying, "She's very matter of fact, very straightforward. My character is dealing with the guilt of leaving a crew member behind, but she's still responsible for the lives of five other crew mates. I tried to play her as Tracy would have been in those moments."[8] Damon prepared for the role by a different method: "For me, the rehearsal process was sitting with Ridley and going kind of line-by-line and moment-by-moment through the script and playing out a plan of attack for what we wanted each scene to accomplish."[9]
The Media Action Network for Asian-Americans (MANAA) criticized the casting of white actor Mackenzie Davis as Mindy Park, whom it said author Andy Weir had described as Korean-American. The group also criticized the casting of Chiwetel Ejiofor as Vincent Kapoor, whom the organization said Weir described as an Asian Indian character. In the novel, the character's name was Venkat Kapoor, and he identifies religiously as a Hindu (a Baptist and a Hindu in the film). The group described these casting decisions as whitewashing, part of a broader phenomenon that deprives Asian actors of opportunities.[6] Weir said in October 2015 he perceived Mindy Park as Korean but said he did not explicitly write her as Korean. He also dismissed criticism of Ejiofor's casting, saying that Kapoor is "an American. Americans come from lots of different sources. You can be Venkat Kapoor and black."[7] He said his novel intentionally avoided physical descriptions of his characters.[7]
Naomi Scott was cast and filmed as Ryoko, a member of the JPL team. Her scenes were removed from the final cut.[10]
