What was J.K. Rowling’s first novel written for adults under her own name?

J.K. Rowling’s first adult novel published under her own name was The Casual Vacancy.

Little, Brown published the novel in 2012, five years after the final Harry Potter book. Set in the fictional English parish of Pagford, it begins when a local council member dies unexpectedly, creating a vacant seat and exposing conflicts involving class, poverty, drugs, and family life.

The book is unrelated to the Wizarding World. It is a realist social novel with an ensemble cast rather than a fantasy adventure centered on one young protagonist. Rowling used the story to explore adult institutions and the effects of political decisions on an ordinary community.

The Cormoran Strike novels are also adult fiction, but they were published under the pseudonym Robert Galbraith. That distinction makes The Casual Vacancy the relevant answer when the question specifies publication under Rowling’s own name. The novel was later adapted into a BBC television miniseries.