Before the First Curse
As young boys, Liam travels with his brother Killian and their father Brennan onto a ship. Unbeknownst to them however, is that their father is a fugitive on the run. He trades his sons into the Captain's servitude in exchange for a row boat and flees, leaving Killian behind, along with a half-asleep Liam, who is unaware of what has just happened.
Now a grown man, Liam and Killian are in servitude aboard Captain Silver's ship. Wishing to be free, Liam signs himself and Killian up for positions in the Royal Navy, but fails when he discovers that Killian, in a drunken state, gambled away their money for freedom. Approaching Captain silver with their release papers, Liam requests that he and Killian be let go. Captain Silver points out what Killian has done, saying Liam is allowed to leave, but Killian will be required to stay behind. Outraged, Liam tears up the papers and throws them overboard.
A few days later, the crew is riding straight into a hurricane, when Liam and the others request to Captain Silver to plot another course, he refuses, saying he is searching for the treasure known as the Eye of the Storm. Liam, Killian and a majority of the crew stage a mutiny against Captain Silver, successfully taking over the ship. While Liam begins to map a new course for the ship, Hades appears to him, asking for the "precious cargo" (the souls) aboard the ship. Liam holds a sword to Hades, ready to kill him, however Hades tells Liam that he is immortal, and offers him a deal: let the ship sink and Hades would spare Liam and Killian's lives and also give them the Eye of the Storm, which would allow them to petition the king for a position in the Royal Navy.
Accepting Hades deal, Liam keeps the ship on it's current course. The ship gets wept up in the hurricane and sinks. Hades keeps his deal and allows Liam and Killian to wash ashore, where they are greeted by members of the Royal Navy. Liam presents them with the Eye of the Storm and they are offered positions aboard the Jewel of the Realm.
While working for the Royal Navy, Liam later becomes the Captain of the Jewel of the Realm. The King summons him to travel to Neverland, in search for a plant called Dreamshade, which he believes has the magical property to heal any injury. He chooses his brother Killian to help him navigate him in his journey and gifts him with a sextant. Liam shows Killian a diary with unidentified star charts, and reveals they are travelling to a new land. At this moment, an enemy ship is spotted, steering in the same direction towards his ship. Liam orders his crew to deploy the Pegasus, and reveals to Killian a sail, woven entirely from the mythological flying horse, enabling their ship to fly. The ship lifts from the sea, removing the danger of the enemy ship to Liam and his crew.
The ship arrives on the island, where the brothers come face to face with Peter Pan. Liam ask Pan for the location of the Dreamshade, who reveals to them that it is the deadliest plant on the land. Ignoring Pan's warning, Liam reassures Killian that the Dreamshade isn't a poison. The two eventually come across the plant, with Pan's help. Having found it, Liam and Killian about the plant and it's effects. Holding a higher status than Killian, Liam orders his brother as Captain to do what he says, though Killian refuses. Determined to prove their King is man of honor and that he sent them on a legitimate mission, Liam cuts a vine from the plant, and allows it to pierce his skin, much to the dismay of Killian. Black veins begin to cover the cut around Liam's arm and he falls to the ground, with poison infecting his body. Liam apologises to Killian and dies.
After he is killed, Liam's spirit is sent to the Underworld, due to having unfinished business.
After the Third Curse
Liam is working as a bartender in the Underworld when he learns that his brother has arrived. After hearing the rumors of his arrival, Liam searches for his brother until he finds him at Emma's Underworld house. After getting reacquainted, Killian asks Liam if he knows of a way to defeat Hades. Liam tells them that those who have tried to defeat Hades before have mentioned a storybook that would contain Hades' weakness. Liam had tried searching for it in the past but was unsure where to look. When Emma realizes it is Henry's storybook, they go to her parent's Underworld apartment to search for it. While there, her mother finds a trunk, saying this was where she found it during the First Dark Curse. When they find that the trunk does not contain the book, they continue to search the rest of the apartment. As Emma searches the bedroom, Liam enters, saying he wants to talk to her. He tells her he does not think she is good enough for Killian as Liam believes it is Emma's fault that Killian succumbed to the Darkness, as Killian has been fighting it his entire life and Emma pushed him over the edge. He accuses Emma of being selfish and tells her to let Killian go.
Henry enters the apartment and tells them he encountered the Apprentice and found out that the book is hidden in the Sorcerer's mansion. As Snow White and David leave with Henry to retreive the key to the Sorcerer's mansion, Liam warns them to go about their usual business as Hades has spies everywhere and they would find it odd if Liam was seen with the rest of the heroes.
Later, while Liam is cleaning glasses at the bar, Hades arrives and asks him to get rid of his story that is in the book. When Liam asks why he should help him, Hades threatens that he will reveal Liam's secret deal with Hades aboard the ship to his brother. Liam reluctantly agrees to the deal. After the heroes get inside the Sorcerer's mansion, Liam finds the book, and tears out the pages containing Hades' story, before he tells the others he found the book. He then goes outside to dispose of the pages in a well. Emma confronts him outside, saying that she knows he lied to his brother, but they are soon interrupted by Killian. Emma and Killian talk and Emma walks off after Killian tells her he should stay in the Underworld. Liam stops his brother from going after Emma, and Killian discovers Liam was lying to him, as there is ink from the pages on his hands. When Killian asks why he would lie to him, Captain Silver approaches with the rest of the ship crew saying that Liam has bigger secrets he is hiding.
Captain silvers crew tie up the brothers and take them to the cross-over point. Captain Silver is about to push them over the cliff when Hades appears, and sends Silver over the cliff. Hades then says that Liam will get to live because he held up their bargain, but Killian will die. Liam steps in front of Killian telling Hades he won't let him hurt his brother. Hades then blows Liam over the cliff, and Killian grabs his hand to stop him. Saying he needs to make amends, Liam lets go of his hand and falls into the fires below, but lands on a boat rising from the flames. Their surroundings transform into a peaceful ocean with a ship in the distance. Killian leads all the other sailors to the boat as well, but does not get on, telling Liam that he still has unfinished business with Emma. Liam understands and asks Killian to apologize to Emma for him. The brothers shake hands and Liam and the others sail off to the ship in the distance, heading off to Mount Olympus.