Carbon-based electrode substrates are key components in electrochemical systems, yet they are almost exclusively derived from fossil resources, which contrasts with sustainability and circular economy principles. In this work, lignin is investigated as a renewable precursor for the fabrication of free-standing carbon electrode substrates. Lignin-based solutions are processed by electrospinning to obtain fibrous mats, which are subsequently converted into carbon through thermal treatment. The incorporation of oxidized carbon nanotubes is explored as a strategy to tune the structural and electrochemical performance of the resulting lignin-derived mats. The materials are characterized in terms of morphology, porosity, surface chemistry, and structural order. Their performance as electrode substrates is evaluated under realistic electrochemical conditions using the glycerol oxidation reaction (GOR) as a representative biomass-derived anodic process and directly compared with a commercial fossil-derived carbon paper at identical catalyst loading.