Set in the 'not too distant' future, social class in Gattaca is defined by genetic formation. Eugenics, the process of conceiving children through genetic manipulation, is the most common avenue of giving birth. Although discrimination is illegal, the analysis of D.N.A is common and those who are naturally born are considered 'invalids' and are relegated to menial jobs. Vincent Freeman is one of the last babies to be conceived naturally. When he is born, doctors inform his parents of his numerous genetic shortcomings and he is given an estimated lifespan of 30.2 years. Vincent is then treated as being 'critically ill' and his parents ardently believe that any minor incident has the ability to take his life. Vincent's younger brother, Anton, is conceived by genetic selection and is Vincent's genetic superior. Anton is considered to be worthy of his father's name because he does not have any genetic shortcomings. Vincent dreams of a career in space but is prevented from getting into the training program due to his status as an "invalid."
The two brothers often play a self-invented game called "chicken." This game can also be seen as defining the relationship between the two brothers, where the one who was deemed superior drowned and was saved by his genetic inferior. Both of the brothers swim out into the sea and the one to turn around and swim back is deemed the loser. One day, Vincent finally wins a game of chicken and saves Anton when he starts to drown. Vincent runs away from home.
Vincent works a menial cleaning job at the Gattaca Aerospace Corporation and conceives a plan to gain employment at Gattaca by using DNA samples from an Agent. The agent takes Vincent to Jerome Eugene Morrow, who is a former star athlete that became paralyzed due to his suicide attempt after coming second in the swimming world championships. The contract between them is simple: Marrow will give him his elite genetic status in society while Vincent will maintain Marrow's luxury lifestyle. To avoid detection, Vincent must meticulously groom and clean himself every day to avoid leaving traces of his own genetic material and must carry samples of Jerome's DNA to pass genetic screenings. Vincent excels in Gattaca as soon as he has Jerome's genetics. He is only asked for his urine sample, which is proof of his genetic superiority, at his job interview and is given a lucrative position at Gattaca.
Vincent meets Anton again after the authorities are called in to investigate a murder in Gattaca one week before Vincent's space launch to Titan. Vincent is entrenched in controversy as he is considered the top suspect. The brothers meet during the investigation, and Anton challenges him to a game of chicken. Once again, Vincent wins and takes both of the brothers back to safety using celestial navigation.
During this time Vincent becomes close to his work colleague, Irene Cassini, due to the investigation. Even though she is one of the most talented people in Gattaca, she is unable to go on the Titan mission due to her defective heart. Vincent encourages Irene to overcome her genetically faulty heart and find her self-confidence. This enables the two to fall in love. Jerome gives Vincent a note to keep on the morning of his launch and tells him to read it after takeoff after revealing he has created enough D.N.A samples to last Vincent two lifetimes.
But one final genetic test awaits Vincent before his launch. He is stunned to discover that Dr. Lamar, the doctor in charge of conducting background checks has been aware of his true status. Lamar allows Vincent to keep his genetic validity because of his son, deemed genetically perfect but not so in reality. When Vincent opens Jerome's note, he finds a lock of his hair. Meanwhile, Jerome dons his silver medal and incinerates himself in his luxury home's incinerator.