Ace Ventura (Jim Carrey) is a private investigator living in Miami, Florida, who specializes in retrieval of tame or captive animals. Despite the success of his methods, he does not often receive many assignments and therefore cannot pay rent or repair his battered 1970s Chevrolet Monte Carlo; whereas his eccentricities make him the laughingstock of the Metro-Dade Police Department.
At Joe Robbie Stadium, Snowflake, a Bottlenose Dolphin mascot of the Miami Dolphins, is kidnapped two weeks before the team is due to play in the imminent Super Bowl, whereupon the team's owner Mr. Riddle, believing the team will fear to lose the Super Bowl unless Snowflake is returned, orders his Head of Operations Roger Podacter (Troy Evans) and Chief Publicist Melissa Robinson (Courteney Cox) to find Snowflake. Ventura is hired to solve the case and discovers his first clue in the form of a rare triangular-cut orange amber stone, which he speculates to have fallen from a 1984 AFC Championship Ring. Ventura then tries to find his culprit by tricking each player who played in this competition into showing their rings; but the attempt fails.
Later, Podacter mysteriously falls to his death from his apartment, which Robinson and Ventura go to investigate. Although Miami Police Lt. Lois Einhorn (Sean Young) insists it was suicide, Ventura proves it was murder, embarrassing Einhorn. While trying to find how Podacter's death is connected to Snowflake's disappearance, Ventura learns of a former Dolphins player named Ray Finkle, whom he has not investigated, who had missed the potentially game-winning field goal kick at the end of the Super Bowl XVII, causing the Dolphins to lose the game and his own career to fail.
Having discovered Finkle's obsession with fellow-player Dan Marino, whom Finkle blames for his loss, Ventura is sure Finkle is the culprit, but cannot find him. Ace and Melissa go to a mental hospital where Finkle was last seen; where under the guise of a mental patient, Ace searches Finkle's belongings and discovers a newspaper article about a missing woman, coincidentally named Lois Einhorn. Studying this, Ventura realizes that Lt. Lois Einhorn is Finkle in disguise.
Ventura then follows Finkle to an abandoned dock, where he finds a kidnapped Marino and Snowflake. When the police arrive, Finkle orders the cops to shoot Ace; whereupon Ace tries to expose Finkle by ripping off her clothes, but fails until assisted by Marino.
Marino and Snowflake return in time for the Super Bowl XXVII between the Miami Dolphins and Philadelphia Eagles. At halftime, Ventura attempts to capture an albino pigeon earlier sought by himself, but is prevented by Swoop, the Eagles' mascot. Enraged, Ventura beats the mascot and is thanked on the JumboTron for saving Marino and Snowflake.