The depletion of natural resources has dictated the need to seek alternative feedstock for the manufacture of high added-value products for industrial use. Here we present a road map for the manufacture of activated carbon submicron- and nanofibers from renewable and waste resources, namely lignin and recycled PET (r-PET). Using the electrospinning technique, mats of varying average fiber diameter were prepared, consisting of a varying mass ratio of lignin/r-PET. The carbonization of these mats proved that the morphology of the carbonized fibers depends on the average fiber diameter and on the lignin/r-PET mass ratio of the precursor ones. Using a 1/1 lignin/PET mass ratio results in the melting of the thinnest fibers (average diameter <300 nm). The melting of the thinnest fibers compromises their surface area, while the thicker ones retain their morphology and after activation their surface area can reach the value of 500 m2/g. Using a higher lignin/PET mass ratio (at least 4/1) results in carbon nanofibers with average diameter lower than 200 nm, as the precursors retain their shape after carbonization.