Kate is the eldest of the Mundy sisters and behaves as a mother figure towards the others. As a schoolteacher, she is the only wage-earner in the house, but her reputation as 'The Gander' in the schoolroom is seen to extend into the household. She is a fiercely devout Catholic, indicated by her distaste for the pagan practices at Lughnasa and Jack's loss of faith. However, her sensitivity is evident throughout the play.

In place of a career, Maggie acts as the chief family homemaker. Throughout the play she is revealed as serving a deeper purpose as the joker of the family, defusing tensions as they arise. She cheekily challenges Kate's authority by calling her 'Kitty', whilst being her confidant at the same time. Maggie is seen to have dreams of her own when she learns of her best friend's success. Her sudden quiet contemplation in her monologue is deeply contrasted with her usual fun-loving way of speaking.

At 26 years old, Chris is the youngest of the Mundy sisters, and, like Maggie, has no paid job. Gerry Evans fathered her son, Michael, seven years ago and is seen as walking in and out of their lives as he chooses. As a result, Chris fluctuates between falling into a deep depression when he leaves, yet being renewed with optimism that his next visit will be a permanent stay. Her lack of income can lead Chris to be defensive on the upbringing of her son.

Rose is 32, but behaves much younger than her years, due to a developmental disability. This condition makes her particularly vulnerable to an unseen character, Danny Bradley, a married man, whom Rose believes is in love with her. However, her sisters believe that Bradley is exploiting Rose's simple nature for his own gain. She is particularly close to her older sister, Agnes, with whom she knits gloves to sell in the town.

Agnes is quiet and contemplative, knitting gloves with Rose whilst also helping to keep the house in order, along with Maggie. She appears to be silently infatuated with Gerry and is quick to leap to his defence.

Michael does not appear onstage as a child, but his presence is alluded to by the other characters, while the adult Michael speaks his lines from the side of the stage. As a child, Michael is seen as being surrounded by love, since all five of the sisters dote on him. Michael also acts as a narrator, not only dictating the action as it goes on, but revealing the futures of the other characters in the play.

Gerry is initially portrayed as an intensely negative character for having left Chris after fathering her illegitimate son, Michael. However, upon his first appearance in the play, Gerry is shown to be charming and genuinely affectionate towards Chris. His current job as a gramophone salesman represents his freedom, in sharp contrast to the stagnant lives of the Mundy sisters. This is made all the more obvious by the fact that he is leaving Ireland to join the International Brigade and fight in the Spanish Civil War.

Jack is in his late fifties. He had left home as a young man to work as a missionary in a leper colony in Uganda. Beyond this, he had been a Catholic chaplain in the British Army in East Africa during World War I. He is well respected in Donegal for his missionary work in a leper colony. However, his sudden return to Ballybeg for undisclosed reasons has paved the way for great changes. He has difficulty with his memory, often forgetting the names of his sisters or confusing them with his former house boy Okawa, with whom we are told he was very close.