The reinforcement of rubber by a co-filler system of carbon black and lignin-coated nanocellulose fibrils (LCNF) is investigated. Natural rubber (NR)–polybutadiene (BR) blend compounds containing LCNF loadings of up to 20% of the total filler package are prepared, and the dispersion state of the LCNF is determined using interferometric and electron microscopy. The LCNF is found to be well dispersed on macro- and micro-dispersion length scales, with discrete fibrils tending to align in the milling/calendering grain direction. Cure properties—scorch, rate, and total yield of crosslinks—are unaffected by the presence of LCNF in the compounds. Tensile to break and cyclic tensile properties are found to be reasonably consistent with those of a conventional all carbon black control compound. Tear and laboratory abrasion resistance properties are maintained versus the control compound, while a systematic and substantial reduction in compound Payne Effect with increasing LCNF content is observed. Basic aging properties of the compounds are unaffected by the presence of LCNF. The potential benefits of LCNF as a lightweight, sustainable, and bio-derived reinforcing filler are outlined.