Shuggie is a sensitive, effeminate boy growing up in the gritty, working-class environments of Glasgow. Deeply empathetic and meticulously tidy, he is fiercely devoted to his mother and constantly monitors her moods to keep her safe. His delicate nature and love of dancing make him a target for neighborhood bullies, driving his lifelong struggle to fit the traditional mold of masculinity expected by his society.

Agnes is Shuggie's glamorous but deeply troubled mother. Often compared to Elizabeth Taylor in her striking beauty, she cares intensely about appearances and maintaining outward dignity. Beneath her polished exterior of catalog clothes and uncomfortable dentures, she battles severe alcoholism and depression, using drink to escape a dissatisfying marriage and bleak economic conditions.

Big Shug is Agnes's second husband, a charming but cruel taxi driver who works the night shift across Glasgow. He is highly vain and uses his unearned confidence to seduce women, frequently carrying on affairs while at work. He expects traditional masculinity from his sons and treats his marriage as a game of dominance, aiming to break Agnes's spirit.

Leek is Agnes's son from her first marriage and Shuggie's older half-brother. Tall and thin with his grandfather's distinctive nose, Leek copes with his turbulent home life by staying out of sight in a hidden pallet fort. He possesses a natural talent for art and dreams of attending art school, though his mother's instability and the need to earn money frequently disrupt his ambitions.

Eugene is a large, red-haired taxi driver who lost his previous job when the local coal mines shut down. A widower who lost his wife to cancer, he feels profoundly lonely until he meets Agnes. Well-intentioned but misguided, he attempts to take care of Agnes's family and acts as a traditional masculine influence for Shuggie, though his fundamental misunderstanding of addiction proves dangerous.

Catherine is Agnes's oldest child from her first marriage. She takes a job as an assistant at a credit-lending firm to help support the family financially. Practical and exhausted by the dysfunction in her household, she seeks an escape route from her mother's spiraling behavior, leaving her siblings behind to secure her own future.

Lizzie is Agnes's mother, a pragmatic and hardened woman who houses Agnes's entire family in her small flat. She is highly critical of Agnes's life choices and drinking habits, despite keeping her own hidden stash of alcohol. Her harsh exterior masks a difficult past of surviving poverty and wartime deprivation.

Wullie is Agnes's father, a man who dotes on his daughter and spoils her when he can. Having grown up in a massive, poor family and served in the war, he wants to shield Agnes from hardship. He acts as the ultimate peacemaker in the family, though his leniency enables some of Agnes's bad habits.

Leanne is a tall Catholic girl who grows up with several brothers and attends St. Mungo's. Like Shuggie, she carries the heavy emotional burden of caring for an alcoholic mother. Hardened by her circumstances but fiercely loyal, she provides Shuggie with a rare space where he can drop his guard.

Joanie works as the radio dispatcher for the Northside Taxis company. She becomes intimately involved with Big Shug, eventually allowing him to move into her crowded home, which sets her in direct conflict with Agnes.

Colleen is a religious mother of a large family living in the Pithead housing scheme. She takes pride in her intact household but struggles with the pressures of poverty, her strict religious beliefs against contraceptives, and a wandering husband. She views Agnes with intense suspicion.

Jinty is a coarse, nosy neighbor in the Pithead housing scheme who seems related to everyone in town. She frequently drops by Agnes's house uninvited, using friendship as an excuse to drink Agnes's alcohol and pressure her into partying, actively worsening Agnes's addiction.

Birdy is one of Agnes's new neighbors in the mining town. Blunt and rough around the edges, she quickly diagnoses Agnes's drinking problem and offers her illicit substances, representing the pervasive despair of the town.

Jamesy, often called Big Jamesy, is Colleen's husband and a resident of the Pithead housing project. Unemployed following the local mine's closure, he spends his time lingering in the neighborhood and taking advantage of vulnerable situations.

Moira is Leanne's mother, whose severe alcoholism has left her homeless and destitute in Glasgow. She refuses her daughter's help and serves as a living reflection of the devastating toll addiction takes on families.

Brendan is Agnes's Catholic first husband and the biological father of Catherine and Leek. He provides child support for a time and attempts to maintain a relationship with his children until Agnes deliberately pushes him to his breaking point.

Donald Jr. is Big Shug's nephew. He proposes to Catherine in a highly performative manner and plans to move to South Africa to work in the palladium mines, offering her a convenient ticket out of Glasgow.

Mr. Darling is an older tenant in Mrs. Bakhsh's run-down boarding house. He takes an unwanted sexual interest in Shuggie, adding to the precariousness and danger of Shuggie's independent living situation.

Francis is one of Colleen's aggressive sons. Raised in a chaotic environment, he relentlessly torments Shuggie for his effeminate behavior, using physical violence and homophobic slurs to assert dominance.

Keir is a handsome, confident boy living in the East End flats. He tries to help Shuggie act more traditionally masculine to attract girls, ultimately facilitating Shuggie's introduction to Leanne.

Annie is a young girl living in a caravan with an alcoholic father. She shares a brief, sympathetic bond with Shuggie over their mutual experiences with addicted parents and lets him play with her plastic pony collection.

Ian, known as Lamby, is a single man used by Jinty for his ability to purchase beer. He is briefly set up with Agnes during a drunken afternoon gathering that quickly ends in physical sickness and disaster.