Managing the environmental impacts associated with livestock production is a challenge for farmers, public and regulatory agencies. Sustainable solutions that take into account technical and socioeconomic factors are needed. For example, the comprehensive control of odors, ammonia (NH3), hydrogen sulfide (H2S), and greenhouse gas (GHG) emissions from swine production is a critical need. Stored manure is a major source of gaseous emissions. Mitigation technologies based on bio-based products such as biochar are of interest due to the potential benefits of nutrient cycling. The objective of this study was to test non-activated (non-functionalized) biochar for the mitigation of gaseous emissions from stored manure. Specifically, this included testing the effects of: (1) time; and (2) dosage of biochar application to the swine manure surface on gaseous emissions from deep-pit storage. The biochar surface application was tested with three treatments (1.14, 2.28 and 4.57 kg·m−2 manure) over a month. Significant reductions in emissions were observed for NH3 (12.7–22.6% reduction as compared to the control). Concomitantly, significant increases in CH4emissions (22.1–24.5%) were measured. Changes to emissions of other target gases (including CO2, N2O, H2S, dimethyl disulfide/methanethiol, dimethyl trisulfide, n-butyric-, valeric-, and isovaleric acids, p-cresol, indole, and skatole) were not statistically significant. Biochar treatment could be a promising and comparably-priced option for reducing NH3emissions from stored swine manure.