A biochar made from woody waste feedstock with low-ash content was blended with carbon black (CB) as filler for styrene–butadiene rubber. At 10% total filler concentration (w/w), composites made from 25% or 50% biochar showed improved tensile strength, elongation, and toughness compared with similar composites filled with CB. This demonstrates the potential to use renewable biochar as a partial substitute for CB in flexible, low-filler rubber composite applications.