Liam rarely spoke in the beginning and was often seen doing normal kid stuff.
He gets along well with his older siblings, who often had to shield him from bad influences since he was the only normal member of the family. In return, Liam respects and loves all his older siblings for what they did.
While he originally thought little of his father Frank, he is one of the few Gallagher children to actually partake in the latter's activities. As Liam gets older, he becomes more attached to Frank because he is more of a father-figure to Liam than he was to any of the other Gallagher kids. Though Liam is aware of his father's shortcomings, he does love him and was happy when Frank helped him in enrolling in private school and put in the effort to bond with him. Father and son are shown to make a good team, as Frank invites him on his scams with Liam even giving helpful input. Liam once stated he missed Frank, when the latter was away. Although this wasn't believed, his later actions seem to confirm this was true. Besides picking up Frank's views, Liam has also inherited his father's manipulations and was able to successfully get supplies for Ian's welcome home party, nearly succeed in a scam, and trick Frank into going to Ian's wedding. From the latter part, it can be seen that Liam does not want Frank to be excluded from happy times and was happy to see him partake.
At first, he didn't do well in his initial time in private school, but after Frank helps him this changes and he is given a proper education. As a result, Liam has picked up some skill from his upper class peers and is now more outspoken and intelligent. Liam is the second smartest of the Gallagher kids as he excels in school.
Later, he seeks to embrace his heritage but is shown to go over the top with his attempts by making demands with his sister. He is also dismayed at being bullied by it. After spending time with his mother’s extended family, Liam initially was happy about it and got along well with one of them. However, this was too much for him and Liam soon realize that no matter what happened he was still a Gallagher and embraced this side. He cut off ties with the extended family and grew out of his phase.
He is introduced as the youngest of the family and doing nothing but toddler things. Liam has had little dialogue throughout the series due to his young age, but he has been an important plot point for many episodes.
In Casey Casden, Liam is brought to Sheila's house by Fiona and the latter has fun with the infant. Very soon, Liam wanders outside while Sheila searched the house for him. Frank walked by and greeted his son but didn't acknowledge his predicament of being left outside in the cold. Soon Sheila spotted Liam though had difficulty retrieving him because of agoraphobia but Sheila is able to get him before he wanders in the streets. During But at Last Came a Knock, Monica tried to reclaim him to live with her and her girlfriend Roberta for him to have a black parent. Frank consented however, the Gallagher siblings rallied to keep Liam with them.
In Nana Gallagher Had an Affair, Monica and her partner Roberta (Bob) take Liam to the DNA clinic, where they do a paternity test and it reveals that Frank is Liam's biological father. This was a shock to everyone, despite both Frank and Monica being white. The unusual situation is 'explained' by Frank of the family rumors that Frank's mother Peggy had an affair with an African-American musician to conceive him. He surmises that his genes must have skipped a generation in expressing themselves with him but went to Liam. At dinner, Liam is put in the crib but overhears the argument between his parents and the older Gallagher children refusing to let Monica and Bob take him. In the end, Monica gives up Liam to his siblings and leaves after realizing her selfish ways.
In Summertime, Liam was taken as collateral when Frank bet 10,000 dollars he could not pay back but Frank and the other Gallaghers were able to reclaim him.
During his grandmother Peggy's stay in Can I Have a Mother, he doesn't appear with Debbie stating Liam is in daycare. Later on, Frank mentions to Peggy that Liam is actually his son, laughing at this fact. However, Peggy isn't interested in his stories.
In A Bottle of Jean Nate, Peggy takes note of him and bonds with him while laughing as it confirms the affair she had.
Fiona gained legal guardianship over all the Gallagher siblings, including Liam.
During There's the Rub, Liam accidentally got into cocaine left out at the Gallagher home, overdosed, and nearly died. However, he made it to the hospital in time. Subsequently, Fiona was arrested, jailed, and tried for child abuse and possession of an illegal substance. Due to his exposure to a controlled substance during his adolescence, he could possibly have brain damage, leading to developmental disorders.
In Iron City, he is still in the hospital and slowly recovering. Because Fiona was arrested only Frank can get Liam out the hospital, due to him still holding parental rights over the kids. The Gallaghers searched for him and soon found him with their half-sister Samantha Slott and nephew Chuckie Slott. Afterwards, Liam is released with his sister being shocked to see him.
Following his return home in A Jailbird, Invalid, Martyr, Cutter, Retard, And Parasitic Twin, he is tended to by his brothers Carl and Lip who subsequently takes over as guardian of the family until Fiona is back to her senses. Samantha tried to bond with him, as Lip tells her to earn a keep around the house. Fiona also holds her brother and tearfully apologizes to him.
Liam remains in the care of Lip, who is still distrustful of his sister and acts as guardian,
Liam is often seen in the background not doing much, he is often tended to by his family.
In Crazy Love, while his father is suffering a bad reaction from a lack of medication, he asks Liam for help. However, Sammi forbids her younger brother from helping him, since he had it coming. Later on, Liam and his siblings spy on Jimmy Lishman and Fiona. Fiona also mentions Liam's near death experience and how she went to jail for it.
During Tell Me You Fucking Need Me, he and his siblings were surprised to see Sammi shoot their father in the arm.
After Frank recovered in Uncle Carl, Liam would imitate the sound on the day after. Frank took his mockery in stride and laughed with his son.
While Frank was grieving over the loss of his girlfriend Bianca, he admitted his love of his children Debbie, Fiona, and Liam before going out of the house.
Carl once tried to use Liam to impress the father of his love interest but the latter shooed him off.
While Carl was with Dominique Winslow, the girl told Liam to leave out of the room so that she and Carl can have relations.
When Frank returns from the hospital after his coma in Hiraeth, Liam lets him back in the house and is thanked by his father.
During Swipe, Fuck, Leave, when the older Gallaghers kick Frank out and he disowns his children for trying to kill him; Frank decides to take Liam. Lip and Ian try to intervene but Frank states he will only allow Liam to remain his child, since he was the last one to stay on his side as the older Gallaghers warned Liam of Frank's bad habits. However, Frank mostly treats Liam better than he did with the other kids and even defends him from hostile construction workers. Frank also has Liam charm a woman from him and he mostly stays with his father in the latter's old room. Due to him being present, the older Gallagher cannot do anything severe to the upstairs because they don't want him hurt. Liam stays at the house after Frank realizes the older kids have broke through the cement walls.
In Home Sweet Homeless Shelter, Fiona cracks down on her siblings with their keep in the house but states Liam is the only one to get a free pass. When the family find Frank has opened a homeless shelter, they attempt to stop him but Frank tells them to leave him alone because of their acts on him. However, he doesn't extend this to Liam and lets him be apart of his new family.
As of I Am a Storm, Liam is taken by Lip to daycare. At the end, he goes to a party a Patsy's where he spends his time with his siblings and is shown sleeping in the booth.
During The Defenestration of Frank, Frank greets Liam when he returns home. After Carl insults Frank, the latter gets even by telling him of the new luxurious items that his shelter has and takes Liam to enjoy them. Liam is excited and happily goes but doesn't get a chance after the homeless kick Frank out.
When having problems in starting public school in You'll Never Ever Get a Chicken in Your Whole Entire Life, Liam chases a dog and soon finds his father and asks him for advice. Liam ends up attending a private school because of Frank seeing him being bullied by his peers. As thanks, Liam calls Frank a good father and hugs him as he goes off with a proud Frank watching him. Liam also picks up some of Frank's habits, something Fiona and the others note of but are pleased he did some good.
In You Sold Me the Laundromat, Remember?, Frank is allowed to take Liam to school by Ian, which becomes a stepping stone to the latter being accepted again.
During Ouroboros, his mother Monica returns and greets him but Liam doesn't recall her and she has to remind him of who she is. In the days after, Frank tells his son not to be around her and Liam takes his father's advice.
As of Ride or Die, he is mostly seen doing his school work.
In the finale Requiem For a Slut, his mother dies and Liam is present as the family discuss her death plans. He later helps Frank, Debbie, and Carl, in finding Monica's storage unit to gather her belongings. He was initially unsure but his father persuades him into going and they get the meth. Liam is at the house when his maternal grandfather Bill Darrgen visits and fights Frank. He attends his mother's funeral and is mostly silent in the time.
Due to Frank, Liam continues to go to the private school from the previous season, but he's not getting the private school education. Liam is routinely taken out of class to be used as a token black kid while the private school gives tours to perspective parents, making the private school seem "diverse."
He is present when the family faces problems with Eric Stark, Monica's meth partner in God Bless Her Rotting Soul. He goes with Frank to Fiona's apartment and takes part in digging up his mother before they go to the storage unit and pay the man, he is safeguarded by Debbie and Ian when they are threatened. However, Frank defends everyone by intimidating the meth head and Liam leaves with his family.
During Fuck Paying It Forward, Liam lets Fiona's ex-fiancé Sean Pierce in the house and is criticized for it by Debbie. Liam later talks with his brothers about this before Frank comes in, Liam listens as Frank announces that he will spend more of his time with him after he has decided to change his ways because of Monica's death and raise Liam properly, since he is his last chance to be a real parent. This ends up being fun for both of them as the two bond at a car wash. At night, the two are put off by the stank of Carl with grease.
When Liam starts failing school in The (Mis)Education of Liam Fergus Beircheart Gallagher, this warrants attention from Frank who tells the school to stop using Liam as the token child and actually educate him, which works and he does better.
In Icarus Fell and Rusty Ate Him, Frank makes more attempts at bonding with Liam by reading a story to him. Liam also tells him that getting a car might really show he is being fatherly. In the next day, Liam comes home and is very excited that Frank got a car at his advice and they go for a ride, eating snacks. Because of this display, the older Gallagher children are surprised to see how fatherly Frank can be to one of them.
As the only black child, Liam is initially popular until another black child is put in the school though he is still friends with other kids.
After Frank hits rock bottom and goes back to his previous activities, he uses Liam as free labor regularly, but also has Liam gather information on his friends' wealthy families so he can rob them.
As Frank has reverted to his old self, he has Liam give him info on the rich kids in his class. Though Liam is still happy to spend time with Frank, he secretly returns the items back to the owner's children. Very soon, Liam is called into the school's office where he is told because of his father's indiscretions with the mothers of the PTA, they have been forced to kick him out since his tuition staff has backed out. Liam then spends time with Fiona and uses his knowledge from private school to help her in negotiating with real estate investor Max Whitiford. Liam also tries to find a new school to attend but wants to enter another private school since he has gotten use to it.
At public school, he is initially picked on since he came from private school but he uses his intellect to help him as he bribes a boy with helping in his work if he protects him a mean girl named Sissy and other threats. Eventually, Liam is allowed to advanced to sixth grade, much to his delight.
Liam is soon approached by Sissy who apparently comes onto him in a closet. Liam is confused by what's occurred though enjoyed it, as seen when he told Lip. However that night, Sissy decides to move in with him after telling him, she's supposedly pregnant with his child. Fortunately, Carl and Debbie witnessed this bizarre sight and told Liam that he didn't impregnate Sissy, due to the timing. Intervening the sibling tell Lip and kick her out by drugging her and bringing her to a clinic.
Liam helps his father with trying to pick up a new love interest, he is told some things about his mother by a security at the clinic that Frank is interest interested in. Liam is later present when Ian goes to prison for two years, he sadly hugs his brother goodbye and hands him his paper work before watching him leave.
Liam is woken up at two in the morning, he and his siblings investigate the sound in the attic and see its an alarm with a picture of Ian. They realize that he left them a memento and smile at the gesture. He is soon worried for his sister Fiona after Debbie reveals Ford's marriage and Fiona's breakdown. Liam later takes part in helping Carl and his new girlfriend Kelly go over military studies, since Liam couldn't stay home alone and needed someone to help watch his niece Franny. Liam remarks on Carl's cluelessness on most of the subjects but states he is a natural when it comes to harsh background. Liam later watches as a drunk Fiona moves back in the house and goes with his siblings to watch Ford's humiliation, he enjoys Fiona getting revenge on him by shooting paint balls at him.
In BOOOOOOOOOOOONE!,Liam is annoyed when Debbie continues to take charge and shows she is really serious by even having Liam chip in since she and Carl worked at his age. He is also with his siblings ready defend Fiona when Ford comes but is turned away. He bonds with Kev's foster son and makes money with a basic job and tries to pay Debbie but she keeps him out since more was needed. He sits on the porch bench, as Fiona arrives and is locked out too. They talk for a while, with Liam giving his sister advice. Very soon, Liam sees Debbie ultimately relent to letting them back.
In You'll Know Bottom When You Hit It, the Gallaghers note on how Liam is gone.
As of Lost, Liam is at a friend's house, where he gets a call from his family. He decides not to answer, since it took days for them to notice.
During Found, Liam is still at his friends house and is going through a phase of accepting his racial heritage. He is visited by Debbie and Liam reminds her of how she unknowingly gave him permission to stay over. At the end, he agrees to come back but only if his list of demands are acknowledged.
As of We Few, We Lucky Few, We Band of Gallaghers!, six months have passed and Liam has grown up. His hair is in the style of an afro and he goes over the top with embracing his heritage, though his family are friends tell him that he should stop. Indeed, Liam is bullied by his peers for his new behavior, much to his dismay. Very soon, Liam is with his family for the birth of his new nephew Freddie and is happy for his brother Lip.
During Sleep Well My Prince For Tomorrow You Shall Be King, Liam continues to try and find his identity but has no luck. He also goes to Debbie and his brothers for help about why he is different from them. He also wonders if he is a member of their family only to be reminded by Debbie’s of the paternity test done on him that confirms he is Frank’s kid. Liam is also put off by Lip’ attempts to parent Freddie. Much later he helps Carl with going into business with one of his coworkers about a scam. At the end, he and the rest of the family are given money cards by Debbie who hands over control of the house to Frank. Liam is surprised by his sister’s attitude but accepts the gift. Liam also asks his father about why he is different from the rest of his siblings. Frank explains an affair one of the relatives had. Liam is surprised by this even more so when Frank reveals that not only is the relative still alive but lives up the street. He accompanies his father to visit the relative, wondering why he never told him about her. He gets his answer when one of them shoot in the air when seeing Frank.
During "Adios Gringos", Liam accompanies Frank while he tries to sell one of Carl's babies to an african-american couple. Frank gets the couple to book a suite for him, Liam and the baby. As they are staying in the hotel room, Frank and Liam bond by ordering room service for a cleanup. They proceed to spilling food everywhere. Liam enjoys the time with his father and nephew. The day after that the african-american couple steals the baby. While Frank is devastated, Liam just poaches what´s left in the hotel room.
In Gallavich, Liam wonders if Frank will come to the wedding but the older Gallaghers don't want Frank there. Liam then wonders on what kind of gift to get Ian and Mickey. Liam gets an idea and visits his father, he tricks Frank into thinking that Lip sold the house and they drive Faye's car there. However, Frank discovers Liam was lying and tells Frank to go to Ian's wedding, as Frank refused and tried to leave but he finds Liam stole the keys and Frank begrudgingly goes to the wedding. Liam is pleased by Frank enjoying the times, but disgusted by him making out with the bar's owner who was his old fling.
- According to Frank, Liam took his first steps when he put him down and Liam nearly walked on a railroad track but the wind of the train knocked him down before he could make it.
- He is one of the few characters who likes Frank even after seeing his ways.
- He is younger than his nephew Chuckie Slott.
- Besides Lip, he is one of the most intelligent of the Gallagher children.
- Like his father and brother Lip, he is bilingual.
- He is the only Gallagher child to not attack Frank.
- According to himself, he is skilled in mathematics.
- As of season 10, Liam is the last of Frank’s kids to call him “Dad”.