Phytophthora blight has become one of the most serious threats to the vegetable industry. Managing this disease is challenging, because the oomycete pathogen responsible, Phytophthora capsici, can move rapidly through crop fields, has a wide host range, is resistant to many commonly used fungicides, and produces resilient spores that can survive in soil for up to 10 years. Recent studies have demonstrated that biochar amendments can suppress infection by many soil-borne pathogens—indicating that these amendments could have the potential to help control phytophthora blight. In this study, greenhouse trials were conducted to determine whether two commercially available biochar amendments could suppress P. capsici infection in sweet bell pepper (Capsicum annuum) using three naturally infested field soils. Soil biological and chemical assays were conducted to evaluate whether potential changes induced by biochar amendments were correlated with suppressive activity. Amending soil with a biochar product that included a proprietary mix of beneficial microorganisms and enriched substrates resulted in lower soil P. capsici abundance in all soils, and lower percent root infection in two of the soils tested. This product also resulted in higher soil pH, and lower soil nitrogen availability and leaf chlorophyll content. The other biochar product did not suppress P. capsici, and had few effects on soil chemical and biological properties. Results of this study indicate that some commercially available biochar amendments have the potential to help mediate phytophthora blight, but further trials are needed to confirm that suppressive effects will be observed in field trials. Additional research is also recommended to identify the mechanisms regulating biochar-mediated suppression of phytophthora blight to develop products that can reliably suppress soil-borne diseases in the field.