The pyrolysis of water hyacinth is gaining attention and acceptance as a resource recovery technique due to its availability and economic viability. However, the presence of lignin, one of the three major biomass fractions, presents significant challenges for profitable water hyacinth processing for biofuel production. Fungal pretreatment of water hyacinth for lignin breakdown has been explored but the application of Trichoderma atroviride as a pretreatment for pyrolysis is relatively novel. The efficacy of T. atroviride pretreatment in improving water hyacinth's pyrolytic products using a fixed‐bed reactor was therefore investigated in this study. The optimization process was studied using a central composite design in response surface methodology with Design Expert 13. Delignification of the biomass was established because the elemental analysis showed a 25.42% increase in cellulose content and a 23.40% and 3.37% decrease in lignin and hemicellulose content, respectively. The biomass pretreatment applied influenced the physical and chemical characteristics of the pyrolytic products. The highest pyrolysis oil yield increased by 25.81% at 575 °C and particle size 2290 μm, and the highest char yield decreased by 4.23% at 273 °C and particle size 1500 μm. This research is crucial for policy and research conversations as it offers a scientific basis for the application of T. atroviride pretreatment in biomass pyrolysis technology and emphasizes the optimal utilization of water hyacinths to obtain socio‐environmental benefits.