This work examines the feasibility of co-gasification of sewage sludge and paper-mill sludge in a commercial scale plant and its application for sludge-to-energy conversion. The results indicated that the thermal reaction activity is increased with an increase in the amount of sewage sludge. This is due to the sewage sludge contains less fixed carbon content could decrease the activation energy, resulting in a thermal reaction is significantly enhanced. The synthetic gas (syngas) composition, that includes H2 and CO, ranged from percentages of 2.59%–4.13% and 3.2%–6.91%, respectively. The heating value of the produced gas ranged from 1.67 MJ/Nm3 to 2.56 MJ/Nm3, which was coupled with cold gas efficiency (CGE) that ranged from 46.6% to 77%. In the case of two tons of wet tested sludge with 67% moisture content, it could produce one ton of dry tested sludge with 30% moisture content after a drying process, and produce approximately 2.2 tons of syngas in gasification. After using a boiler and heat exchanger for energy recovery, it is possible to recover 4.46 tons of steam. This steam could provide energy for the dryer, and constitutes a positive sum on the energy balance in a commercial scale gasification plant.