Ace Ventura is an unorthodox Miami-based private detective who specializes in retrieving tame or captive animals. He struggles to pay his rent and is often mocked by the Miami Police Department, led by Lieutenant Lois Einhorn, who finds Ventura insufferable. Two weeks before the Super Bowl, the Miami Dolphins' mascot, a bottlenose dolphin named Snowflake, is kidnapped at Joe Robbie Stadium. Melissa Robinson, the team's chief publicist, hires Ventura to find Snowflake.
Searching Snowflake's tank for clues, Ventura finds a rare triangle-cut orange amber stone in the filter. Ace suspects billionaire Ronald Camp may have stolen Snowflake, as he is known for collecting exotic animals through less-than-reputable means and sources. Ventura and Melissa sneak into Camp's party, where Ventura mistakes a shark for Snowflake and is nearly eaten. Camp apologizes and shakes Ventura's hand, revealing on one of his own fingers a ring with an amber stone set identical to the one Ventura found. Ruling out Camp, as his ring was not missing the amber stone, Ventura recognizes the stone as part of a 1984 AFC Championship ring and concludes that a member of the 1984 Miami Dolphins line-up may have kidnapped Snowflake, and attempts to identify the culprit by their rings. However, he discovers all of the team members' rings are intact.
Roger Podacter, the team's head of operations, mysteriously dies after falling from his apartment balcony. Einhorn declares it a suicide, but Ventura proves that it was murder because the soundproof balcony glass doors were closed when the police arrived despite a neighbor claiming to have heard screaming. He comes across an old photograph of the football team, discovering an unfamiliar player named Ray Finkle, who was added as a placekicker in mid-season. Finkle missed a relatively easy field-goal kick at the end of Super Bowl XVII, which cost the Dolphins the championship and ruined his career. Visiting Finkle's parents, Ventura learns that Finkle blamed quarterback Dan Marino for allegedly mishandling the ball before the kick, and became so fixated on this that he was committed to a mental hospital for homicidal tendencies. Marino himself is kidnapped shortly thereafter. Ventura visits Einhorn, pitching his theory that Finkle kidnapped both Marino and Snowflake in an act of revenge, as he was offended that the dolphin has been given Finkle's old team number and a field-goal trick to boot; he also theorizes that Finkle murdered Podacter when the latter discovered him snooping around his apartment. Einhorn compliments Ventura and kisses him before attempting to dissuade him from continuing the case since there is now a suspect, but Ventura refuses since he is still under contract by the Dolphins to locate Snowflake.
Ventura and Melissa go to the mental hospital, where Ventura poses as a potential patient. Ventura uncovers a newspaper article in Finkle's possessions about a missing hiker named Lois Einhorn. Piecing together the evidence, Ventura, to his shock and disgust, realizes that Einhorn is Finkle: Finkle underwent plastic surgery to take on the identity of the missing Einhorn, and took advantage of her position in the Miami Police Department to get revenge on Marino and the Dolphins. On Super Bowl Sunday, Ventura follows Einhorn to an abandoned yacht storage facility where she has Marino and Snowflake held hostage. Einhorn calls the police, blaming Ventura with no proof. Melissa and Ventura's friend, police officer Emilio, suspecting the deception, stage a hostage situation to get the police to listen to Ventura. To prove Einhorn is Finkle, Ace strips her of her clothes and, with help from Marino, reveals that Einhorn never got the penectomy and vaginoplasty necessary to perfect the disguise; Podacter discovered this during a date with Einhorn and was pushed off the balcony to stop him from revealing this to the public.
Einhorn/Finkle is arrested by the police after attacking Ventura, and her ring is confirmed to have the stone missing. Marino and Snowflake are welcomed back during half-time at the Super Bowl; Ventura is then shown on the stadium's jumbotron and acknowledged as their savior, even as he gets into a scuffle with the Philadelphia Eagles' mascot Swoop over a rare pigeon, receiving a large ovation from the crowd.
Jim Carrey as Ace Ventura
Courteney Cox as Melissa Robinson
Sean Young as Lt. Lois Einhorn / Ray Finkle
Tone Loc as Emilio
Dan Marino as Himself
John Capodice as Sgt. Aguado
Noble Willingham as Riddle
Troy Evans as Roger Podacter
Raynor Scheine as Woodstock
Udo Kier as Ronald Camp
Frank Adonis as Vinnie
Tiny Ron as Roc
David Margulies as Doctor
Bill Zuckert as Mr. Finkle
Judy Clayton as Martha Mertz
Alice Drummond as Mrs. Finkle
Rebecca Ferratti as Sexy Woman
Mark Margolis as Mr. Shickadance, Ace's landlord
Randall "Tex" Cobb as Gruff Man
Cannibal Corpse as themselves
started a franchise, spawning the sequel film Ace Ventura: When Nature Calls (1995), the animated television series Ace Ventura: Pet Detective (three seasons, 1995–2000), and later, standalone made-for-television sequel Ace Ventura Jr.: Pet Detective (2009).