Biochar is increasingly acknowledged as a multifunctional material for sustainable waste valorisation. Biochar is applied to enhance bioprocess stabilisation (anaerobic digestion, AD). It is produced through pyrolysis at different temperatures, and as a result, biochar develops distinctive surface properties. However, the underlying mechanism of biochar in AD remains unclear. This research implements a systematic investigation to correlate biochar production and physicochemical characteristics with AD of simple and complex substrates. Rice husk is the primary biomass source for biochar, an abundant agricultural residue in Asia. The research includes three parts: AD pre-treatment, covering biochar production and characterisation; AD process of substrates; and AD post-treatment, evaluating microbial and chemical adsorption after AD is finished to understand biochar’s role throughout the whole cycle. Comparison between pre-mixing inoculum with biochar in advance and later together with substrates is also investigated for AD stabilisation. The use of simple and complex substrates will elucidate which metabolic steps are most influenced by biochar. Pre-mixed inoculum and biochar have been found to accelerate the methane production compared with the later addition of biochar together with substrate. It is likely due to biofilm maturation before substrate addition, thereby optimising substrate degradation. This research would contribute to advancing AD performance by also integrating biosolids production, i.e. biochar from rice husk, across the overall AD process.