In his first appearance, Eric, along with his man-servant Grimsby and crew of sailors are enjoying another day sailing out in the sea. Eric overhears sailors talking about King Triton, ruler of the merpeople, which makes him curious, but Grimsby brushes it off as nonsense.
One night, as Eric is celebrating his birthday out in the sea, it is revealed through a dialogue between him and his man-servantGrimsby that the kingdom is eagerly awaiting the day that Eric marries. Eric has turned down at least one princess as a prospective bride, the princess of Glowerhaven, claiming that he is still looking for the right girl. When a storm hits and lightning sets the ship ablaze, everyone manages to escape to the lifeboat, but Eric, climbs back onto the burning ship to save his pet sheepdog, Max who was been trapped. He manages to toss the dog into the sea, but he is stuck aboard due to his foot trapped on a hole as the fire reaches some explosives on the ship, causing the ship to explode. When Ariel finds an unconscious Eric in the water, she drags him to shore and sings to him, but before he can fully regain consciousness, Max and Grimsby arrive, forcing Ariel to dive underwater. Eric tells Grimsby that the former has been saved by a girl with the most beautiful singing voice, but Grimsby, thinking Eric has swallowed too much seawater, carries him back to his palace.
When Eric is seen again, he is on the beach outside his palace with Max, still haunted by Ariel's singing voice and playing Ariel's song on his flute, and has been searching the kingdom for her. But then Max starts to bark excitedly and run off, making Eric follow the dog, who leads him to Ariel, who has been transformed into a human by Ursula. He initially finds her familiar, but her lack of a voice, due to Ariel trading her voice for a pair of legs, makes him think that she cannot be the girl who rescued him. However, he brings her back to his palace and they spend time together. After some advice from Grimsby, Eric takes Ariel on a tour of his kingdom. That evening, the two go on a boat ride in which Sebastian leads a group of animals in a chorus of "Kiss the Girl" in an attempt to get Eric to fall in love with Ariel and kiss her, so that she can remain human. Just as the two come close to kissing, Ursula's eels, Flotsam and Jetsam intervene by tipping over their boat.
That night, as Eric plays Ariel's song on his flute, Grimsby advises Eric to forget about his "dream girl", and focus on the one "warm, caring, and right before his eyes". He apparently does so, throwing his flute into the sea. But before he can approach Ariel, Ursula, who has transformed herself into a human girl named Vanessa arrives and uses Ariel's voice trapped in her seashell to hypnotize Eric into believing she is the girl who saved his life, causing him to forget all about Ariel. Eric almost marries Vanessa, but before the vows are completed, Ariel's seagull friend Scuttle learns Vanessa's true identity and leads the same group of birds and sea creatures that sung to Ariel and Eric on a mission to stop the wedding while Ariel, with the help of her companion Flounder, swim to the wedding ship. During the chaos, the seashell around Vanessa's neck is smashed, freeing Ariel's voice, which is restored to its owner. Eric, who has come out of the spell, realizes that Ariel is the girl he has been looking for.
But before they can kiss, the sun sets, and Ariel is transformed back into a mermaid. Vanessa transforms back into Ursula, takes Ariel as her prisoner, and dives into the ocean. Determined not to lose Ariel again, Eric goes after them, diving into the sea to help Ariel. He hits Ursula with a harpoon, and Ursula instructs her pet eels Flotsam and Jetsam to strangle Eric, but Flounder and Sebastian extricate him. Ursula attempts to finish Eric off with a trident she has gotten from King Triton, but due to Ariel's intervention, she accidentally destroys her eels instead. Eric and Ariel attempt to escape from an enraged Ursula, who enlarges herself into a giant. Ursula then separates Eric from Ariel as she traps the mermaid princess in the bottom of a whirlpool Ursula has created. While Ursula is concentrating on finishing Ariel, Eric climbs onto one of the shipwrecks that has surfaced as a result of the whirlpool, takes control of the ship and steers it toward Ursula who is about to destroy Ariel by using the trident. Suddenly, Eric kills Ursula by plunging the ship's splintered bow through her belly, saving Ariel, as well as the entire underwater kingdom of Atlantica, and ending her reign of terror in the process. Ursula, while also being backfired by the energy of the trident, uses her last breaths to bring the ship down with her, but Eric jumps off in time.
Eric manages to reach the shore, and collapses from exhaustion. When he wakes up, he sees Ariel, transformed back into a human (courtesy of King Triton), and the two embrace finally kissing for the first time. The film ends with their wedding, at which Eric and Ariel exchange vows, and Triton accepts Eric as his son-in-law.