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 little dialogue throughout the earlier seasons due to his young age, but he has been an important plot point for many episodes throughout the series.
In Casey Casden, Fiona brings Liam to Sheila's house, which excites Sheila. Very soon, Liam wanders outside while Sheila searches the house for him. Frank walks by and greets his son but does not acknowledge that he is left outside alone in the cold. Soon Sheila spots Liam outside, but has difficulty retrieving him because of her agoraphobia. Sheila is ultimately able to get him before he wanders in the streets by tethering herself to the house with sheets. During But at Last Came a Knock, Monica tries to take Liam to live with her and her girlfriend Roberta, who goes by Bob, so he can have a black parent. Frank consents to this, but the Gallagher siblings rally to keep Liam with them.
In Nana Gallagher Had an Affair, Monica and her partner Bob take Liam to the DNA clinic, where they do a paternity test and it reveals that Frank is, in fact, Liam's biological father. This is a shock to everyone because both Frank and Monica are apparently white. Frank "explains" the situation with the family rumors that Frank's mother Peggy had an affair with an African-American musician to conceive Frank. He surmises that the genes must have skipped a generation in expressing themselves. At dinner, Liam is put into the crib for the night, but is disturbed by the argument between his parents and the older Gallagher children who refuse 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 is taken as collateral when Frank can not pay back a $10,000 bet, but Frank and the other Gallaghers are eventually able to reclaim him by offering Kevin's excess weed plants instead.
During his grandmother Peggy's stay in Can I Have a Mother, he does not appear because he is in daycare according to Debbie. Later, Frank mentions to Peggy that Liam is actually his son, laughing at this fact. However, Peggy does not appear interested in his stories.
In A Bottle of Jean Nate, Peggy notices Liam and bonds with him while laughing, seemingly confirming the family rumors.
Fiona gains legal guardianship over all the Gallagher siblings, including Liam.
During There's the Rub, Liam accidentally gets into cocaine that Fiona left on the living room table. He is taken to the hospital for the overdose and almost dies, but ultimately survives. Subsequently, Fiona is arrested, jailed, and tried for child abuse and possession of an illegal substance. Due to his cocaine ingestion, the doctors tell his family that Liam could possibly have brain damage, leading to developmental disorders.
In Iron City, he is still in the hospital and slowly recovering. Because Fiona is arrested only Frank can get Liam out the hospital, as his legal father. The Gallaghers search for Frank and soon found him with their half-sister Sammi Slott and nephew Chuckie Slott. Afterwards, Liam is released, and Fiona is shocked but relieved to see him.
Following his return home in A Jailbird, Invalid, Martyr, Cutter, Retard, And Parasitic Twin, Carl and Lip tend to Liam, and Lip takes over as guardian of the family until Fiona is back to her senses. Sammi tries to bond with him after Lip tells her to earn her keep around the house. Fiona later holds Liam and tearfully apologizes to him.
Lip is still distrustful of Fiona and continues to care for Liam at college with the help of Amanda.
Liam is often seen in the background, not doing much besides being cared for by his family.
In Crazy Love, while his father suffers a bad reaction from a lack of medication, he asks Liam for help. However, Sammi forbids Liam from helping Frank, 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 her time in jail as a result.
During Tell Me You Fucking Need Me, Liam and his siblings are surprised to see Sammi shoot their father in the arm.
After Frank recovers in Uncle Carl, Liam imitates the sound the next day. Frank takes the mockery in stride and laughs with his son.
While Frank grieves the loss of his girlfriend Bianca, he declares his love for his children Debbie, Fiona, and Liam before leaving the house.
Carl tries to impress Dominique's father by bringing Liam to her house.
Dominique tells Liam to leave the boys' bedroom so that she and Carl can have sex.
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 because he was the only one to not have a part in throwing Frank into the lake. The older Gallaghers warn Liam of Frank's bad habits. However, Frank treats Liam better than he did with the other kids, for the most part, and even defends him from hostile construction workers. Frank also directs Liam to charm a woman for him. Liam stays with Frank in Frank's old room after Frank blocks off the second story of the house with cement blocks. Due to Liam's presence, the older Gallaghers cannot do anything severe to Frank or the second story because they don't want him Liam. Liam stays at the house after the older Gallaghers break through the cement blocks.
In Home Sweet Homeless Shelter, Fiona cracks down on her siblings, forcing them to earn their keep in the house by paying rent and utilities, but states Liam gets a free pass because of his age. When the family learns that Frank has opened a homeless shelter, they attempt to stop him but Frank tells them that he has disowned everyone except for Liam. Instead, Frank allows Liam be a part of his new family.
During The Defenestration of Frank, Frank greets Liam when he returns home. After Carl insults Frank, Frank brags about the new luxurious items that have been donated to his shelter and takes Liam to the shelter with him. Liam is happily goes with Frank to the shelter, but the homeless kick Frank out before they can enjoy it because Frank has been stealing from the donations.
Fiona allows Liam to walk to his first day of public school in You'll Never Ever Get a Chicken in Your Whole Entire Life, but finds the school doors locked. A sign on the door indicates that the students will instead be taken to a different school on school buses. Liam cannot read the sign, and instead chases a dog and soon finds Frank and asks for advice. Frank gets Liam into a private school for free after going on a tirade about the private school's superiority complex and harm to public schools. The school waives tuition for Liam, apparently because the school wants to appear diverse. 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, which Fiona and the others notice but are nonetheless pleased that Frank got Liam into a good school.
In You Sold Me the Laundromat, Remember?, Ian reluctantly allows Frank to take Liam to school, which becomes a stepping stone to Frank being accepted by the family again.
During Ouroboros, his mother, Monica, returns and greets Liam, but he does not remember her, and she has to remind him of who she is. In the days after, Frank tells his son not to go around Monica 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, Monica dies, and Liam is present as the family discuss her burial plans. He later helps Frank, Debbie, and Carl, in finding Monica's storage unit to gather her belongings. He is initially uncertain, but Frank persuades him to go in, and they take a large amount of meth from the unit. Liam is at the house when his maternal grandfather Bill Darrgen visits and fights Frank. He attends his mother's funeral and does not say much.
Liam continues to attend the private school that Frank got him into, but Liam is routinely taken out of class by the school administration to be used as a token black kid during tours to perspective parents, allowing the school claim that it is "diverse."
Liam 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 to find out what she did with his portion of the meth. Liam later takes part in digging up his mother to retrieve the unsold meth and goes with the family to the storage unit to repay Eric. Debbie and Ian stand in front of Liam to protect him when Eric threatens them with a gun. However, Frank defends everyone by intimidating Eric, 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 Parent-Teacher Association, 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 that 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 deceitful ways.
- He is younger than his nephew Chuckie Slott.
- Along with Lip, he is one of the most intelligent of the Gallagher children.
- Like Frank and 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 refer to him as Dad.