In the English-speaking world, he is best known for writing The Phantom of the Opera (Le Fantôme de l'Opéra, 1910), which has been made into several film and stage productions, such as The Phantom of the Opera, starring Lon Chaney and a novel by Susan Kay called Phantom, based solely on his work.

Leroux went to school in Normandy and studied law in Paris, graduating in 1889. He inherited millions of francs and lived wildly until he nearly reached bankruptcy. Then in 1890, he began working as a court reporter and theater critic for L'Echo de Paris. His most important journalism came when he began working as an international correspondent for the Paris newspaper Le Matin. In 1905 he was present at and covered the Russian Revolution. Another case he was present at involved the investigation and deep coverage of an opera house in Paris, later to become a ballet house. The basement consisted of a cell that held prisoners in Paris Commune, which was the government during the French Revolution.

He suddenly left journalism in 1907, and began writing fiction; in 1919, he made his own film company, Cinéromans. He first wrote a mystery novel entitled Le mystère de la chambre jaune (1908; The Mystery of the Yellow Room), starring the amateur detective Joseph Rouletabille. The Mystery of the Yellow Room is considered an important work in the history of detective fiction due to its being the first "locked-room puzzle," which has become a staple in the genre. Leroux's contribution to French detective fiction is considered a parallel to Edgar Allan Poe's in America and Sir Arthur Conan Doyle's in the United Kingdom.