On Writing is organized into five sections, each with a different focus. The first section is a curriculum vitae ("C.V.") which is an autobiographical account of King’s life and his early exposure to writing. King talks about his early attempts to get published, and his first novel Carrie. King also talks about his fame as a writer, and what it took to get there. This section includes his relationship with his wife, the death of his mother, and his history of drug and alcohol abuse. The second section is titled "What Writing Is". He briefly introduces himself again and includes an example of literary description. King compares writing to telepathy and urges the reader to take writing and his advice seriously. In the third section, "Toolbox", King discusses English mechanics and the importance of vocabulary, grammar, and style in writing. The fourth section, "On Writing", details King's advice on writing. The fifth section, "On Living: A Postscript", is also autobiographical. King discusses the 1999 accident in which he was struck by a vehicle while walking down an isolated country road. He describes the injuries he suffered, his painful recovery and his struggle to start writing again.

King includes part of a rough draft and an edited draft of his story "1408". He also includes a poem by his wife Tabitha King.

In the United Kingdom paperback version, a short story by Garret Adams entitled "Jumper" was included at the end of the book. The story won the On Writing competition.