Organic waste generation and energy resource depletion have become pressing issues that must be addressed. In this regard, adopting waste-to-energy technology is critical for managing organic wastes and producing renewable energy. Anaerobic digestion (AD) is among the most popular technologies that have provided dual benefits of waste treatment and alternative energy generation. It has been commonly used to treat various types of organic waste, such as agricultural waste, livestock manure, and wastewater sludge. However, the low biodegradation efficiency, operating temperature, and special gas handling requirements limit the applications of AD technology. The recent research mainly focuses on enhancing biogas production and biodegradation efficiency. Several studies have proved that the use of conductive additives in the AD matrix has improved biodegradation and biogas production performance. The types of conductive additives have a significant effect on the efficiency of AD. Therefore, this study aims to - (i) synthesize a novel conductive composite additive from granular activated carbon (GAC) coated with nano zero-valent iron (nZVI) by the co-precipitation method, (ii) characterize the surface morphology and conductive behavior of the synthesized conductive materials, and (iii) identify the effects of conductive materials addition on the efficiency of biogas production and biodegradation in AD. Hence, thermophilic AD (TAD) was operated under three different conditions such as (i) addition of GAC/nZVI materials in the matrix of TAD, which was operated for co-digestion of cow manure with food wastes (ground rice and bread); (ii) addition of GAC/nZVI materials in the matrix of TAD, which was operated for mono-digestion of cow manure; and (iii) the control TAD without the addition of GAC/nZVI materials in the TAD matrix, which was operated for co-digestion. Biogas production increased by 11 folds upon using GAC/nZVI in the TAD matrix compared with the control TAD without additives. Moreover, the addition of GAC/nZVI increased the methane contents (%) in biogas by 20.7 folds compared with the control TAD. This is because the addition of conductive materials in the AD matrix increased the electron transfer between the organisms, which enhanced microbial communication and growth. However, the addition of conductive materials in the TAD matrix did not enhance the methane production when operated with only cow manure (mono-digestion). This is because the cow manure possessed significantly less biodegradable nutrients for the acetogenic and methanogenic microbes. The findings revealed that the addition of GAC/nZVI conductive materials in the TAD matrix has a significant effect on the co digestion of cow manure blended with food wastes for methane production, COD removal, and pH stabilization.