The film was loosely based on the traditional tale "Jack the Giant Killer" and features extensive use of stop-motion animation. The film was directed by Nathan H. Juran and later re-edited and re-released as a musical by producer Edward Small. The reason for the change to music was on the grounds that Columbia Pictures, which released The 7th Voyage of Sinbad, threatened to sue Small. The original print without the music got released 30 years later with no protest from Columbia Pictures, while United Artists continues to own the rights to the musical version of the film. The film brought together Mathews, Juran, Small, and actor Torin Thatcher, all four of whom worked on 7th Voyage.
In the Duchy of Cornwall of fairy tale days, a malevolent sorcerer named Pendragon, ruler of giants, witches, hobgolins, and all evil creatures, was defeated by the wizard, Herla, and along with his disciples, exiled to an uncharted, unknown island. Pendragon, however, vows revenge and Herla dies, meaning a threat against Pendragon no longer exists. Years later, the kingdom celebrates the crowning of Princess Elaine (Judi Meredith). The reception goes well until Pendragon (Torin Thatcher) arrives disguised as a foreign lord; as a birthday gift, he gives Elaine a magical music box with a small anthropomorphic jester inside that walks and dances and which unbeknownst to Elaine is Pendragons giant minion Cormoran. When Elaine is asleep later that night, Pendragon uses his magic to turn Cormoran back to his full size and captures Elaine. The castle guards try to stop the giant, but he overpowers them with relative ease and escapes. Cormoran takes Elaine to a ship, but before it can sail, a brave farmer named Jack (Kerwin Mathews) rescues Elaine; Jack then fights Cormoran and kills him. In gratitude, King Mark (Dayton Lummis) makes Jack Elaine's protector and entrusts him to safely guide her to a convent across the sea. What he does not know, however, is that Elaine's waiting-maid, Lady Constance (Anna Lee), is actually a witch in league with Pendragon and reveals the king's plan to him.
Enraged at having his plan foiled, Pendragon makes up another one, determined to stop Jack. While Jack and Elaine are planning their trip, King Mark and his servants discuss the potential danger that is now Pendragon. While Jack and Elaine are falling in love during their journey, Pendragon sends his demonic witches to intercept Jack's ship. In the chaos, the ship's captain (Robert Gist) is murdered and Elaine is captured, and when Jack attempts to follow the kidnappers, the crew, spooked by the creatures, mutiny and cast Jack and his friend Peter (Roger Mobley), the captain's young son, overboard. At his castle, Pendragon uses his powers to turn Elaine into an evil witch, then returns to Cornwall and confronts King Mark, telling him he has one week to renounce the throne and let Elaine rule alongside Pendragon, or she will die. After he vanishes, Mark realizes Constance has betrayed him, and when she stands before a mirror, she appears as a witch. King Mark then breaks the mirror, thereby freeing Constance from Pendragon's power.
In the sea, a friendly old Viking named Sigurd (Barry Kelley) rescues Jack and Peter and introduces them to the Imp (Don Beddoe), a leprechaun imprisoned in a bottle by the king of the elves for crafting seven-league boots from his pot of gold. The Imp explains that his three remaining gold coins can each grant a wish to one with a pure heart, on the condition that Jack break open the bottle to free him once all three are used up. With the use of the Imp's first two wishes, Jack manages to approach Pendragon and coerce him into giving Elaine back, unaware that she has been transformed and now holds allegiance with them. Upon their return journey, Elaine disables Jack with a sleep potion, but when she touches the Imp's bottle, it grows hot because of her evil nature, causing her to accidentally cast it into the sea. Pendragon captures Jack and his friends and attempts to make him tell the whereabouts of the leprachaun by turning Peter and Sigurd into a chimpanzee and a dog, respectively. When Pendragon cannot force Jack's compliance, he leaves him with Elaine, who finally reveals her witch form to him. With Peter and Sigurd's aid, Jack manages to break free and smash Elaine's mirror reflection, restoring her to normal.
As the friends flee the castle, Pendragon sends a giant similar to Cormoran (but this time with two heads) to block their path. As they retreat, they find the Imp washed ashore, who grants Jack's final wish by summoning a sea monster, which kills the two-headed giant. As a last resort, Pendragon transforms himself into a dog-like dragon and attacks the ship, but Jack kills him in a fierce battle. In effect, Pendragon's death causes the destruction of his castle, crushing Garda, the hobgoblins and the witches in the process, while Sigurd and Peter are restored to human form. Jack then honors his promise and frees the Imp from his bottle, and the leprechaun uses his boots to return to Ireland while giving Jack and his friends a lead for their triumphant return to Cornwall.
Kerwin Mathews as Jack
Judi Meredith as Princess Elaine
Torin Thatcher as Pendragon
Walter Burke as Garna
Don Beddoe as Imp
Barry Kelley as Sigurd
Dayton Lummis as King Mark
Anna Lee as Lady Constance
Roger Mobley as Peter
Robert Gist as Scottish Captain
Tudor Owen as Chancellor
Ken Mayer as Boatswain
Helen Wallace as Jack's mother (uncredited)
The fairy tale had been previously filmed by Hollywood in 1917, 1924 (a short), 1931 (a cartoon), and 1952.
Edward Small announced the film in 1959, saying he had developed the special effects over two years. Filming was originally meant to be started in September 1959, in 70-mm and widescreen, but was delayed several more years.
The film was partly shot on Catalina Island.
Stop motion effects were done by Jim Danforth.
Reviews were generally positive.
A film directed by Bryan Singer and starring Nicholas Hoult was released on March 1, 2013, titled Jack the Giant Slayer. It had previously been announced as titled Jack the Giant Killer, but it is not a remake of the 1962 film, but a reworking of the traditional story Jack and the Beanstalk with elements from other stories such as Jack the Giant Killer.