Food waste is an underutilized organic resource given its abundance and high potential energy. The purpose of this study was to confirm the suitability of pyrolyzed food waste as a co-firing fuel by adjusting the pyrolysis temperature (300–500 °C) and retention time (15–60 min). Both high moisture (compost) and low moisture (feedstuff) food waste were examined. Increasing the temperature and retention time yielded more volatile H and O as well as C sequestration, resulting in reduced H/C and O/C ratios. Notably, the van Krevelen diagram increased in similarity to that of coal. Upon pyrolyzing food waste compost, more than half of the chloride was volatilized, the highest carbon content of the compost and feedstuff were 61.35% and 54.12%, respectively, after pyrolysis at 400 °C for 60 min; however, the calorific value of the pyrolyzed feedstuff was reduced owing to the high salt concentration. The pyrolyzed compost and feedstuff had high Ca contents, which contributed to an increased ash fusion temperature. Therefore, food waste byproducts are advantageous as co-firing fuels in terms of energy regeneration. Nevertheless, further research is required regarding the removal of salt and alkali earth metal ion materials.