The first season takes place on the day of the California Presidential Primary.

The season's main plot revolves around an assassination attempt on David Palmer, a U.S. Senator from Maryland who is a presidential candidate for the Democratic Party, on the day of the primary election in California. The central character is Jack Bauer, a former United States Army Delta Force operator, who is the Director of the fictional Counter Terrorist Unit (CTU) in Los Angeles. Bauer becomes professionally as well as personally involved when his wife Teri and daughter Kim are kidnapped by the people behind the assassination.

The season is divided into two halves; the first revolves around a mercenary group's efforts to control Jack Bauer by kidnapping his wife and daughter and forcing him to kill Senator Palmer. This culminates in Jack's successful rescue of his family. In the second half, a second wave of assassins is discovered. As CTU tracks their activities, Jack learns why he and the Senator are being targeted, and motions to counter against the assassins.

Fox initially ordered only 13 episodes—the successful rescue at the end of the season's first half was planned as a series finale in the event that the show was not renewed.