What was J.K. Rowling’s first novel published for adults?

J.K. Rowling’s first novel published for adults was The Casual Vacancy.

Published by Little, Brown and Company in 2012, The Casual Vacancy is a standalone novel set in the fictional English town of Pagford. Its story begins after the sudden death of Barry Fairbrother, a parish councillor, and examines tensions involving class, politics, family life and local institutions.

The book was Rowling's first major novel after the completion of the seven-book Harry Potter series. It differs sharply in tone from Harry Potter: it is contemporary literary fiction for adults and deals with difficult social subjects. That contrast led many readers to treat it as a deliberate break from her earlier work.

The Casual Vacancy was later adapted into a three-part BBC television drama in 2015. It should not be confused with Rowling's later crime novels, which she published under the pseudonym Robert Galbraith.