Using a tapa cloth to animate her story, Gramma Tala (Rachel House) tells a group of young children the story of the mother island Te Fiti. With her heart, Te Fiti possesses the power to create life and brings other islands into existence. However, other beings desired the power of her heart but only one was daring enough to take it. The demigod Maui (Dwayne Johnson), using his magical fish hook to shape shift into various creatures, travels to the mother island and steals Te Fiti's heart; a small, green gemstone engraved with a spiral. Without her heart, Te Fiti's island begins to deteriorate and sends forth a terrible darkness. Maui escapes on his boat but is confronted by Te Ka, a demon of lava and fire which rose from the sea like a volcano. Maui boldly engaged Te Ka in battle but was struck from the sky, losing both his hook and Te Fiti's heart to the sea.
Gramma Tala finishes her story saying that, a thousand years later, Te Ka and other monsters still hunt for the heart while the darkness continues to spread until, one day, it will consume their island. At this, most of the children either cry or faint, but one girl is spellbound. Gramma Tala then says that, one day, someone will find the heart, journey beyond the island's reef, find Maui, and take him to restore the heart and save everyone.
At that moment Chief Tui (Temuera Morrison), the little girl's father, enters and tells the children that there is no darkness or monsters and they are safe on their island as long as they stay within the reef. However, he accidentally hits a post that reveals multiple cloth paintings of monsters, sending the children into a panic. In the chaos the little girl, Moana (Louise Bush), slips away and goes down to the water. She sees a seashell wash up on shore and goes to collect it when she notices a baby sea turtle being menaced by a group of frigate birds. Leaving the shell, Moana shields the turtle with a large leaf and guides it to the water's edge. Once it's safe, a rippling effect washes over the surface of the ocean and the water recedes, revealing a trail of beautiful seashells which Moana gathers in her tiny arms.
Within the canyon of water and surrounded by sea life and coral, a wave forms over Moana's head and looks curiously down at her. It plays with her, splashing her and tying her hair in a topknot. Then, in the water, Moana sees a shiny object drifting toward her. She plucks the glowing green stone from the water and trails her finger over the spiral design. Just then, her father calls for her and the ocean returns her to shore on a piece of driftwood, but Moana drops the stone. Before she can find it, Chief Tui picks her up and takes her back to the village along with her mother, Sina (Nicole Scherzinger). She tells Moana that she'll do wondrous things as the future chief.
Growing up, Moana learns everything she needs to know about life on her island, Motonui (song: "Where You Are"), but she finds herself continuously drawn to the ocean. Every time she goes near it, her parents bring her back and remind her that to her duties and her people are where she belongs; not the sea. Her grandmother, Tala, however, encourages Moana to follow her heart and listen to the 'voice inside'; for that is who she truly is. Chief Tui then takes Moana, now grown, to the sacred peak of their island and shows her a tall pile of flattened stones which he and his forefathers placed to raise the island higher. One day, he says, Moana will place her own stone on the peak.
Moana grows into her role as chief in training despite her inner wish to go to the sea and makes her rounds on the island: she fixes a leaking roof, provides support to a man getting a tattoo, and teaches children hula dancing. An elderly man points out a rooster named Heihei (Alan Tudyk) pecking and attempting to eat a rock and wonders if he should be eaten, but Moana says that, in some cases, one's strength is hidden beneath the surface. Then, a woman shows Moana and her parents that the coconut harvest has yielded blackened, rotten fruit. Moana chooses a new location to plant a grove but then a group of fisherman show the chief that their haul of fish has brought in nothing, despite changing their fishing rounds. Moana suggests fishing beyond the reef, but the notion angers her father who storms off.
Sina goes to Moana and explains to her that Tui's reservation against the ocean comes from his youth when he took a boat to sea and was wrecked in a storm. His friend, who had begged to go, drowned. Tui doesn't want the same thing to happen to Moana but Sina tells her that she must make her own choices, however hard they are.
Conflicted over her duties to her village and her dream to sail the sea (song: "How Far I'll Go"), Moana ultimately decides to finally take a canoe out to see if she can find any fish beyond the reef and takes her pet pig, Pua, with her. At first it seems she can sail with ease, but a wave knocks her canoe sideways and sends Pua overboard. Distracted, Moana fails to see another wave rise above her and flip her canoe over. Moana is submerged and gets her foot trapped within some coral but manages to free herself by smashing it with a rock. She makes it to shore, exhausted, and find Pua scared, but alive. Gramma Tala then walks up joking that whatever transpired should be blamed on the pig. Moana tries to hide her bruised ankle, but Tala isn't fooled and takes a look. However, she promises not to tell Moana's father.
Moana says that Tui was right about going out there. She tells Tala that she's going to put her stone on the pile. Tala doesn't argue and goes to the water to dance with a school of manta rays, saying that when she dies she'll come back as one, or else she chose the wrong tattoo. Curious as to why her grandmother isn't contradicting her, Moana asks if there's something she wants to tell her.
Tala takes Moana to a holed up cavern where, after removing some rocks, Moana finds a passageway. Tala says that Moana has heard all their people's stories but one. She tells her to follow the tunnel and bang the drum to find the answer to the question that's bothered her all her life: who is she meant to be?
Moana follows Tala's instructions and finds a small fleet of boats and canoes hidden in the cavern behind a massive waterfall. She bangs the drum on the largest ship and sees a vision of her ancestors within the tapa sail. It reveals that they were voyagers who sailed the ocean finding new islands to inhabit (song: "We Know The Way"). Thrilled, Moana asks Tala why they stopped voyaging. Tala explains that when Maui stole the heart of Te Fiti and unleashed the darkness it made sailing too treacherous; boats stopped coming back. To save themselves, Moana's ancestors hid away their boats and decided to remain on Motonui. Tala then shows Moana a portion of their island which appears to have the very life from it being drained to sea. She then tells Moana that her stories were true; that someone will one day restore the heart and save everyone. Then, she presses a green stone into Moana's hand that she'd kept within her necklace, saying that she was there the day the ocean chose Moana to be the one to restore the heart. The ocean then rises up and playfully splashes Moana who was stunned to find out that the memory wasn't just a dream as she thought.
Tala shows Moana a constellation of an enormous hook, saying that Maui will be beneath it. Moana laments that she doesn't know how to sail but realizes she knows who does. She runs to the master hut where Tui is addressing the council, trying to assure them they won't run out of food. When Moana interrupts and begs help to restore the heart, Tui leaves in anger and says he should have burned the boats in the cavern ages ago. He takes the stone from Moana's hand, saying it's merely a rock, and throws it into the bushes. When Moana retrieves it, she finds her grandmother's walking stick. Just then, a warrior calls to the chief. Tui and Moana run to their hut to find Tala lying in bed, unwell. Whispering, she tells Moana to take the heart and find Maui. She gives her the necklace to hold the heart in and tells Moana she'll always be with her. Moana leaves and her mother helps her pack. From the cavern, Moana takes the small canoe with a spiral painted on the sail. Once on the water, Moana looks back and sees her grandmother's spirit in the form of a manta ray flying toward her. It illuminates safe passage for her and Moana makes it to the sea.
She struggles to sail properly, following the hook constellation, and even discovers that Heihei has stowed away. One night Moana's canoe capsizes just before a storm hits and Moana is washed up on a rocky island. Angry that the ocean didn't help her when she asked, Moana is still relieved that she didn't lose the heart of Te Fiti. Then, she notices hook-shaped marks dotting the rocks on the island and realizes that the ocean has delivered her to Maui. She ducks behind her canoe as Maui approaches, preparing herself, but Maui easily lifts the canoe with one hand, excited to see a boat. Moana confronts him but Maui interrupts and begins boasting about all his exploits (song: "You're Welcome"), using his Mini-Maui tattoo to show off his accomplishments displayed as numerous tattoos all over his body. Maui tricks Moana and traps her in the cave he lived in while he plans to commandeer her canoe, despite protests from Mini-Maui. Moana escapes the cave and jumps into the ocean as Maui sails away. Moana tries to catch up and is assisted by the ocean which deposits her quickly onto her canoe. Despite repeatedly throwing her overboard, Moana is returned to the boat by the ocean and she demands of Maui that he help her restore the heart.
Maui tries to throw the heart away but the ocean throws it back at him. Then he tries to swim away, but the ocean puts him back. He claims that the stone is not a 'heart' but rather a curse that lost him his hook and that bad things are always trying to find it. At that moment, a spear lands on the boat, just missing Heihei. Behind them a massive object moves out of the fog. Maui recognizes the small coconut creatures and their large ship as Kakamora - tiny, mischievous pirates. Moana begs the ocean to help them, but Maui tells her that the ocean doesn't help; they help themselves. He is shocked to find out Moana can't sail and does all he can to evade the Kakamora, but they latch onto Moana's canoe with their spears and board the craft. They knock Moana down and the heart falls out of her necklace. Heihei gobbles it up but the Kakamora steal him. Maui tries to escape but Moana takes the oar and goes after Heihei. She manages to retrieve him in a flurry of paralyzing blow darts and zip-lines herself back to her canoe. She and Maui just barely escape as the Kakamora's boats collide into each other.
Afterward, Maui is still hesitant to return the heart but Moana convinces him by saying that he would be restored to the hero he once was. She agrees to help him retrieve his hook before setting a course for Te Fiti and then asks him to teach her to sail. At first Maui refuses, but the ocean uses a leftover blow dart to paralyze Maui, forcing him to tell Moana what to do. He shows her how to wayfind, using celestial navigation. They make their way to a tall, rocky spire in the middle of the ocean. At the top is the entrance to Lalotai; the realm of monsters. Maui opens the entrance and he and Moana drop into the realm. Moana evades an array of monsters and eventually finds the entrance to the lair of Tamatoa, a creature Maui said would have his hook since he loves to collect shiny and valuable objects.
Using her as bait, Maui sends Moana into the lair where Tamatoa captures her. While Maui sneaks up from behind, Moana distracts Tamatoa by inciting him to brag about himself and Tamatoa obliges (song: "Shiny"). Maui then takes his hook and attempts to shapeshift, but it's been so long that he can't control his powers. Tamatoa places Moana in a cage and focuses on Maui as he finishes his song. Then, Moana uses some bioluminescent algae to create a false heart of Te Fiti and distracts Tamatoa with it while she and Maui escape. Using a geyser, Maui and Moana are shot back to the surface.
Back on top, Maui is sincere for once, humbled by the fact that he can't shapeshift. On the canoe, he tells Moana that they have no chance of defeating Te Ka, even with his hook back. Moana then asks him about a tattoo on his back that he noticed earlier but Maui is hesitant to talk about it. After some persistence, he gives in and tells Moana he earns his tattoos which show up magically. The one on his back was his first; he was born to human parents but they didn't want him and threw him into the sea. The gods took pity on him and made him the demigod Maui, giving him his fish hook. But Moana tells him that it's not the gods who make him Maui - it's him. With this renewed confidence, Maui tries shapeshifting again, starting small, and this time is able to control his powers.
He teaches Moana how to sail properly and, by morning, compliments Moana on her abilities just as they reach Te Fiti. With the island in view, Moana gives Maui the heart and wishes him luck. He shifts into a hawk and flies toward the island but Te Ka rises up to confront him. Maui is knocked out of the sky once more and retreats to the canoe. Moana tries to sail past Te Ka despite Maui's protest. Te Ka lunges at them and Maui deflects with his hook but the force sends their canoe hurtling back out to sea. When she comes to, Moana finds Maui brooding over his broken hook. Distraught over this, Maui angrily blames Moana for not listening to him and says that one more hit to his hook will destroy it. He says he's done helping her, transforms into a hawk, and leaves.
Saddened, Moana asks the sea why it brought her here and begs it to choose someone else, giving the heart back to it. She breaks down as she watches the heart sink into the depths but then sees a manta ray spirit swimming toward the canoe. Her grandmother appears and offers comfort, saying that if Moana wants to go home, she'll be with her. However, Moana hesitates and realizes that, in her heart, she was meant to do this (song: "I Am Moana"). She sees visions of her ancestors and, with their strength, dives into the sea and retrieves the heart. When she surfaces, her ancestors and grandmother are gone but she prepares the canoe, stows Heihei safely in the cargo, and sails back toward Te Fiti.
At the barrier islands, she tricks Te Ka and speeds past the rocks, using the water to her advantage since Te Ka can't touch it. Te Ka then sends a giant wave her way, knocking her canoe over and is about to hit her with a blast of fire but Maui appears and defends Moana, giving her enough time to make it to Te Fiti. When she gets there, however, Moana finds that the entire island of Te Fiti is gone; the shape of the goddess gouged beneath the water all that remains. Turning back, she then notices a spiral symbol on Te Ka's chest and realizes the truth. Holding the heart above her, she grabs the attention of Te Ka before it's able to deal a blow to Maui, who has by now completely lost his hook. Moana tells the ocean to clear a path for Te Ka to reach her and goes to meet Te Ka face to face.
Moana tells Te Ka that this is not truly who she is. Te Ka's fires go out as she calms down and Moana places the heart back within the spiral on Te Ka's chest. Restored, the lava rock falls away to reveal Te Fiti, lush and green once more. She returns to her island and takes Moana and Maui in her hand. Maui is apologetic for having taken Te Fiti's heart and the goddess rewards him with a brand new fish hook and gives Moana a new canoe to sail in. Then, the goddess is finally able to rest.
Moana asks Maui to come back with her since her people will need a master wayfinder. Maui says they already have one and bids Moana farewell. Moana sails back to Motonui where the flowers and fruit are blossoming again since the darkness has been defeated. She is reunited with her people and her parents. The ocean gives her a pink seashell which Moana places on the sacred mountain before helping her people take the fleet of boats out to begin voyaging once again. She teaches them to sail and wayfind and revels in her new role with her grandmother's manta ray spirit guiding her and Maui flying beside her.