Bacteria responsible for the anaerobic decomposition of lignocellulosic waste biomass play key roles in the global carbon cycle and possess enzymes with potential industrial application. Here, a novel anaerobic, thermophilic, non-spore-forming bacterium, strain m5T, was isolated from methanogenic enrichment cultures obtained from a lab-scale methanogenic landfill bioreactor digesting anaerobic municipal solid waste. Cells were Gram-stain-negative, catalase-negative, oxidase-negative, rod-shaped, and non-motile. The genomic DNA G + C content was 40.92 mol%. The optimal NaCl concentration, temperature and pH for growth were 0.5–1 g.L−1, 45 °C, and at pH 7.0, respectively. The major fatty acids were C14:0, C16:0, C18:0, C18:1 ω9c, and anteisoC15:0. Strain m5T was able to grow in the absence of yeast extract on glucose, fructose, arabinose, cellobiose, galactose, maltose, raffinose, sucrose, lactose, and pyruvate. In the presence of 0.2 % yeast extract, strain m5T grew on wide range of carbohydrates and amino acids, and was able to use complex substrates such cellulose and xylan. Major end products from cellulose and xylan degradation were valerate and propionate. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the new isolate was most closely related to Seramator thermalis SYSU GA16112T (94.42 % 16S rRNA gene sequence identity). Genome-based relatedness as well as both Average Nucleotide Identity (ANI), and Average Amino Acid Identity (AAI) strongly supported that strain m5T belongs to the Dysgonomonadaceae family. Metagenomic analysis of the landfill bioreactor community revealed that the Dysgonomonadaceae family was the most abundant in the constructed bioreactors. Based on its unique genomic features, strain m5T is considered to represent a novel genus, for which the name Anaerorudis is proposed. Moreover, several phenotypic, biochemical, and physiological properties differentiated the novel bacterial strain from related species, indicating that the strain represents a new species for which the name Anaerorudis cellulosivorans sp. nov. is proposed, with strain m5T (= DSM 112743T = ATCC TSD-267T) being the type of strain. This study highlights the biotechnological potential of strain m5T, specifically in the bioconversion of cellulose and xylan, a recalcitrant substrate within lignocellulosic plant biomass, to enhance biogas production.