Here are some of his most notable works:
* The Fatal Secret (1869)
* The Curse of the Diamond (1869)
* The Man Who Won the Lottery (1872)
* The Mystery of the Haunted House (1872)
* The Shadow of the Past (1873)
* The Black Hand (1874)
* The Lost Will (1875)
* The Mystery of the Red Room (1876)
* The Stolen Bride (1877)
* The Haunted Ship (1878)
Southworth wrote prolifically and published hundreds of novels, often using different pseudonyms. His stories were full of action, adventure, mystery, and romance, and they appealed to a wide audience.
While his works are considered to be of historical interest, they are not often read today. They are, however, valuable for their insight into the popular culture of the 19th century.