This acoustic monitoring program deployed twenty marine acoustic recorders off Canada's east coast between August 2015 and July 2017. The recording protocol was selected to monitor marine mammal acoustic occurrence and characterize the underwater soundscapes. The monitored locations ranged from the Scotian Shelf to the southern Labrador shelf through the Grand Banks of Newfoundland. The choice of monitored locations represents a balance between areas of potential interest for oil and gas development and less-sampled locations that were known or presumed to be important to marine mammals. The underwater soundscape and its noise contributors were quantified. Drilling platforms contributed significantly to the local soundscape of targeted areas and were measurable for extended periods to ranges of at least 15 km at the seabed in deep water and 35 km in shallow water. Seismic survey sound was detected over wide areas, particularly north of the Flemish Pass. Vessels were detected at all stations, with the highest vessel sound levels measured at stations near shipping lanes or near active drilling platforms. Sounds from up to twenty-three species of marine mammals were identified acoustically in the data. This included up to six species of the Delphininae subfamily (small dolphins). Stations in the southern parts of the study area maintained high species richness throughout the year, whereas northern stations saw a decline in winter and spring.