Which Harry Potter novel is the longest by word count in its original English edition?

Harry Potter and the Order of the Phoenix is the longest Harry Potter novel by word count in its original English edition.

Published in 2003, Order of the Phoenix contains roughly 257,000 words, making it the largest of the seven novels by English word count. The story follows Harry’s fifth year at Hogwarts, including the Ministry of Magic’s campaign against Dumbledore and the arrival of Dolores Umbridge as Hogwarts High Inquisitor.

The novel is also notable for introducing the student resistance group known as Dumbledore’s Army. Harry, Hermione, and Ron help fellow students learn practical defensive magic while the school authorities restrict the teaching of the subject.

Page counts vary among editions because of typography, paper size, language, and formatting. That is why word count is a more useful comparison than the number of printed pages. The later books may look similarly large in some editions, but Order of the Phoenix remains the longest in English.