Biomethanation of biomass-derived syngas represents a promising bioenergy conversion technology that can be operated within integrated plants to deliver ancillary services such as carbon capture and storage (CCS), seasonal energy storage and fuel densification. In the present study, we developed a set of techno-economic process models considering syngas biomethanation as a core unit complemented by Power-to-Gas (PtG), pure oxygen compression, CCS, and biomethane liquefaction. Four different plant configurations and five operating modes with biomass inputs ranging between 8.4 and 60.2 MW were investigated overall, indicating biomethane yields between 0.16 and 0.48 m3 kg−1 (dry basis). An energy analysis demonstrated how intensive PtG operation delivers substantially higher biomethane cold gas efficiencies (44.4%) compared to operating modes without electrolysis (30%–34.8%). In fact, a small-scale PtG-biomethanation configuration (S-EL) delivers the lowest biomethane minimum selling price (MSP) of 1.63 € m−3. Under existing biomethane subsidies in Denmark and Italy, S-EL would achieve profitability only under stored electricity costs equivalent to approximately 50% of the current levelized cost of renewable electricity generation in the two countries, combined with maximum biomass costs of 50 and 30 € t−1, respectively. All other configurations suffer from high costs and efficiency limitations and would require subsidies equivalent to 126%–348% of the current natural gas consumer price to reach profitability. The study provides evidence to support an intensification of targeted policies that support multi-service plants, and it highlights the need for access to low electricity prices as well as the urgency for low-cost gasification technologies.