This article describes the earliest French oceanographic expeditions dedicated to investigating the deep sea. Though these expeditions, conducted from 1880 to 1883, were quite successful in terms of both science and what today we call “outreach,” they are often overlooked in histories of oceanography or mentioned only in passing. They produced a substantial literature of over 100 scientific publications. Participants’ descriptions of 176 new species are still considered valid today. Among the remarkable scientific discoveries were culturable and pressure-tolerant bacteria in deep-sea sediment samples, which led to the origin of deep-sea microbiology, and iconic deep-sea fish such as the gulper eel. Specimens, instruments, and equipment from these expeditions were on display for the general public at an exhibition at the National Museum of Natural History in Paris in early 1884. Between 1885 and 1891, expedition scientists authored three mass-market books on deep-sea life and the expeditions. Following a summary of the expeditions and their results, some speculation is provided as to why such an auspicious nineteenth century beginning of oceanography in France did not lead to a sustained interest in oceanography. A supplementary file contains a bibliography of expedition publications and a list of the species described from expedition collections.