Early and Middle Devonian fossils from the Sainte-Hélène Island diatreme breccias are criticially reviewed and analyzed stratigraphically. They include marine benthic faunas of Helderberg, Oriskany, Schoharie, Onondaga, and Hamilton ages. Brachiopods are the most abundant fossils; significant corals are also present and are discussed for the first time. These diatreme faunas from the Montréal region significantly augment the lithofacies–paleogeographic data known for this part of North America. For the first time, attention is paid to the lithologies in which the Sainte-Hélène Island faunas are embedded, as clues to the regional relations of these rock types. The absence of Silurian specimens is ascribed to nondeposition similar to that known in the Albany, New York, region to the south. The presence of marine, Hamilton age rocks and fossils at Montréal shows that the Acadian Orogeny and uplift into the nonmarine environment did not affect the area until at least some time in the Hamilton.