Moriarty’s novels center themes of motherhood and family. She is interested in the dynamics between family members, including parents and their children, siblings (young and grown), and—perhaps most of all—husbands and wives. Moriarty is interested in the scenes that unfold behind the closed doors in so-called “normal” suburban families; she often centers her plots on an unexpected event occurring in a familial context. As characters work through their problems, Moriarty explores how they move on from tragedy, heal personal and interpersonal wounds, and learn to live amid life’s complexities.

Moriarty is the eldest of six children, and sibling rivalry is a theme in her work. In interviews, she has mentioned that she began writing because her younger sister published a novel first. Sibling rivalry is evident in What Alice Forgot, as well as in some of Moriarty’s other novels, including Three Wishes, and Apples Never Fall.

Moriarty and her partner underwent numerous attempts at in vitro fertilization (IVF) before Moriarty gave birth to their two children. An interest in infertility is evident in her books, particularly in Elisabeth’s struggles in What Alice Forgot.