A United States Army librarian, Corporal “Average Joe” Bauers (Luke Wilson) is selected for a suspended animation experiment on grounds of average appearance, intelligence, behavior, etc. Lacking a suitable female candidate, they hire Rita (Maya Rudolph), a prostitute whose pimp “Upgrayedd” (Brad “Scarface” Jordan) has been bribed to allow her to take part. The experiment is forgotten when the officer in charge is arrested for having started his own prostitution ring under Upgrayedd’s tutelage. Five hundred years later, Joe and Rita’s suspension chambers are unearthed by the collapse of a mountain-sized garbage pile, and Joe’s suspension chamber crashes into the apartment of Frito Pendejo (Dax Shepard), who expels him.
The former Washington, D.C. has lost most of its infrastructure, with people living in plastic huts called “domistile”. The human population has become morbidly stupid, speak only low registers of English competently, are profoundly anti-intellectual, and are named after corporate products. Suspecting hallucination, Joe enters a hospital, where he is incompetently diagnosed, and comes to realize what has happened to him and to society. He is arrested for not having a bar code tattoo to pay for his doctor’s appointment, and after being assigned the grossly incompetent Frito as his lawyer, he is sent to prison. Rita returns to her former profession.
Joe is renamed “Not Sure” by a faulty tattooing machine, and takes an IQ test before tricking the guards into letting him escape. Once free, Joe asks Frito whether a time machine exists to return him to 2005, and bribes him with promises of riches through compound interest on a bank account Joe will open in the 21st century. Frito knows of one, and leads him with Rita to a gigantic Costco store, where a tattoo scanner identifies Joe. He is apprehended, but is taken to the White House, where he is appointed Secretary of the Interior, on the grounds that his IQ test identified him as the most intelligent person alive.
In a speech, President Camacho (Terry Crews) (a former professional wrestler) gives Joe the impossible job of fixing the nation’s food shortages, Dust Bowls, and crippled economy within a week. Joe discovers that the nation’s crops are irrigated with a sports drink named “Brawndo”, whose parent corporation had purchased the FDA, FCC, and USDA. When Joe has the drink replaced with water, Brawndo’s stock drops to zero, and half of the population lose their jobs, causing mass riots. Joe is sentenced to die in a monster truck demolition derby featuring undefeated “Rehabilitation Officer” Beef Supreme (Andrew Wilson).
Frito and Rita discover that Joe’s reintroduction of water to the soil has prompted vegetation to grow in the fields. During the televised event they show the sprouting crops on the stadium’s display screen, and Camacho gives Joe a full pardon, appointing him Vice President. Joe and Rita find that the “time masheen” Frito had mentioned is merely an inaccurate, history-themed amusement ride. Following Camacho’s term, Joe is elected President. Joe and Rita marry and conceive the world’s three smartest children, while Vice President Frito takes eight wives and fathers 32 of the world’s stupidest children.
In a post-credits scene, a third suspension chamber releases Upgrayedd, who is intent on tracking Rita down.