In order to take action against global warming and ensure a greater energy independence, countries around the world are expected to drastically increase the proportion of renewable energy in their energy mix. However, the intermittent production of energy explains why energy supply and demand do not match. In this context, biomethanation, coupled with anaerobic digestion, could be an interesting approach to transform the extra amount of produced electricity by converting hydrogen (produced by electrolysis) and carbon dioxide (present in biogas) into methane. In this review, we have summarized several recently published results which involve biological methanation processes performed by mixed cultures, with an emphasis on microbiological as well as process aspects. In particular, the different microorganisms involved in the process, as well as the used metabolic pathways, along with their kinetic and thermodynamic specificities, are described. Furthermore, the influence of process parameters such as the type of reactor, the type of diffuser and the choice of H-2 injection (in situ or ex situ) or the different operating conditions are presented. Explanations of the different performances observed in literature are assumed, technical bottlenecks are listed, and possible solutions to overcome these issues are presented. Finally, the current commercial deployment of this technology is discussed through the example of three companies offering different biomethanation solutions.