The study aimed to evaluate the potential use of sewage sludge–derived biochar as a soil amendment and nutrient source. Biochar was produced through torrefaction of municipal sewage sludge collected from a wastewater treatment plant located in the Upper Silesia region (Poland). The process was carried out at 250 °C for four hours under oxygen-limited conditions and atmospheric pressure, yielding a stable, porous material with approximately 80% reduction in initial volume. Chemical analysis of the obtained biochar revealed a high content of organic matter (62.8%), carbon (34.4%), and essential nutrients such as nitrogen (5.7%) and phosphorus (3.1%), along with safe concentrations of heavy metals. To assess the bioavailability of macro- and micronutrients, a pot experiment with a grass mixture was conducted using four treatments: control soil, soil with biochar, soil with ash–sludge mixture, and soil with raw sludge. The results showed that biochar addition significantly enhanced plant biomass production—by approximately 67% compared to the control—indicating its high fertilizing potential and positive influence on soil structure. Furthermore, the torrefaction process ensured complete hygienization of the sludge and degradation of potential organic micropollutants. Sewage sludge torrefaction thus represents a sustainable approach for nutrient recovery and waste volume reduction within the circular economy framework