The global shift toward renewable energy has increased the demand for wood pellets, raising sustainability concerns. Incorporating refuse-derived fuel (RDF) waste into pellets enhances energy output while reducing landfill waste. This study examines the impact of RDF incorporation on the quality of lignocellulosic biomass pellets. The RDF sample was mainly composed of plastics (32%), textiles (16%), and paper (11%), and the pellets were produced in a semi-industrial pelletizer with RDF incorporation rates of 0, 15, 25, 50 and 100%. The pellets were characterized for chemical composition and physical and fuel properties by determination of moisture content, ultimate composition, mineral composition, apparent density, mechanical durability, and calorific value. The addition of RDF improved mechanical durability (97.7–99.5%) and reduced fines content (2.3–0.5%). Although RDF-containing pellets had lower apparent density, light plastics contributed to their strength. Combustion properties were also enhanced, with a 16% increase of the higher calorific value (HHV) of 100% RDF pellets (20.85 MJ/Kg) relative to that of the 100% biomass pellets (17.46 MJ/Kg). Energy density exceeded 10.5 GJ/m3 for all pellets, peaking at 11.5 GJ/m3 for 100% RDF pellets. Despite increasing chlorine levels, RDF addition lowered slagging and fouling indexes, indicating greater stability and reduced deposits. This study highlights RDF’s potential as a valuable additive for pellet production if the biomass mixture is of high quality. This could provide an effective approach for integrating this type of waste into energy production.