In recent years, due to the circular economy, the use of green energy forms, such as biofuels and biogas from anaerobic digestion of fermentable materials (e.g., agricultural and livestock residues) has entered our lives. According to the International Energy Agency it is estimated that the needs in 2040 will be 48% higher than in 2012 so all political decisions have converged on an urgent need for the use of more and more renewable and green energy. Considering the overall economic activity of these sectors in the region of Thessaly, the aim of this study is to highlight the residues from agricultural and livestock activities in the primary sector and calculate the annual biomass production, the methane and biogas potential, the electrical and thermal energy that can be produced from these wastes, as well as the solid residue that can be used to improve the soil of the region. The study was based on data referring to the years 2015 to 2020. The production of livestock and agricultural residues, averaged over the above six-year period in the study area, was estimated at approximately 4.8 × 106 t·yr.−1, with livestock residues accounting for 83% and agricultural residues for 17%. Furthermore, the total residues can produce an average biogas potential of approximately 4.7 × 106 m3·yr.−1, while the amount of electricity that can be produced ranges from 708–1091 GWh·yr.−1, and the corresponding thermal energy from 1112–1577 GWh·yr.−1. As a result of the complete anaerobic digestion process, a solid residue could also be obtained for the improvement of the region’s soil, which translates into a quantity in the range of 4.01 × 104 to 5.10 × 104 t·yr.−1.