Anaerobic digestion of nitrogen-rich organic wastes as the sole feedstock does not only have low efficiency in methane production due to its inherent carbon deficiency (low carbon/nitrogen ratio) but also requires an acclimation period during the startup phase. This study investigated the effects of pyrogenic carbonaceous materials (PCMs), namely, activated carbon and biochar, on dynamic changes in anaerobic microbial diversity and corresponding digestion performance in anaerobic digestion of swine manure during the startup phase of the reactors. The results showed that both activated carbon and biochar changed the microbial communities and enhanced the microbial communities of Archaea, unclassified Bacteroidetes, Bacteroidetes, and YC-E6. Correspondingly, such changes stabilized the digestion of swine manure faster and significantly enhanced digestion performance. The digestion with activated carbon demonstrated better performance than the digestion with biochar due to the larger surface area of activated carbon. Maximum biogas productions were observed in the AD reactors containing 0.25% activated carbon (1134 mL/g VS loaded) and 1% biochar (655 mL/g VS loaded) under the conditions of 20-day HRT. The methane content of the biogas formed was 71% (v/v) in all AD reactors. The results showed that activated carbon and biochar have significant impacts on microbial communities, which help alleviate inhibition from H2S and ammonia and improve biogas production. Under longer hydraulic retention time (20 days), pyrogenic materials were also able to eliminate or shorten the startup phase that is typical for the anaerobic digestion without using an inoculum.