Which novel was J.K. Rowling’s first book for adults?

J.K. Rowling’s first novel for adults was The Casual Vacancy, published in 2012.

The book was released by Little, Brown and Company on 27 September 2012. It is a standalone novel set in the fictional English town of Pagford, where a local council vacancy exposes conflicts involving class, politics, family, and social disadvantage.

The novel marked a deliberate change from the fantasy setting and young-adult readership of Harry Potter. It contains no Hogwarts, magical creatures, or wizarding plot, and its tone is firmly adult literary and social fiction.

The Casual Vacancy was adapted into a three-part BBC television drama in 2015. Rowling later returned to fiction with the Cormoran Strike crime series, written under the pseudonym Robert Galbraith.