Vincent Anton Freeman is the film's main character. He is a "faith birth" or a "god child," because his parents didn't have him genetically engineered to be "the best of both" parents. This makes Vincent an "invalid," and that causes him to be discriminated against by everyone. Even his own family doesn't believe that he is capable of great things. It is why he decides to become a "borrowed ladder" and fake his identity. Vincent uses the genetic profile that belongs to Jerome Morrow.

Jerome Morrow is a valid, and his genetic profile is flawless. He is a former swim champion, but he was hit by a car and paralyzed from the waste down. He willingly helps Vincent achieve the goal of going to space by providing Vincent with genetic samples of all kinds. He says that he got the better end of the deal because he got to experience what it is to have a dream again.

Anton is Vincent's younger, genetically engineered brother. He has a superiority complex due to his engineering, and he later becomes the lead investigator trying to find out how exactly Vincent is or isn't involved in the death of the mission director.

Irene Cassini is another Gattaca employee, and she and Vincent fall in love. She has dreams of going to space as well; however, her genetic profile shows that she has a possible heart condition.

Dr. Lamar is the onsite Gattaca doctor. He knows from the very first day that Vincent is faking his identity in order to be at Gattaca. Audiences figure this out at the end of the film when he tells Vincent, "For future reference, right-handed men don't hold it with their left. Just one of those things." He wants Vincent to achieve greatness because he doesn't believe in the genetic discrimination that exists: it is working against his son, who "isn't all that they promised."