Historically, the majority of agricultural waste generated by various agricultural operations has been either burnt or converted into fertilizer all throughout the world. However, this bulk biomass, which is found all over the planet, offers a tremendous potential for energy generation. The present chapter focuses on hydrothermal liquefaction (HTL), a thermochemical conversion method for turning dry or wet waste agricultural biomass to biocrude oil, charcoal, and gases at temperatures ranging from 200 to 400 °C and pressures ranging from 3 to 25 MPa. Agricultural and forestry biomass comprise plant-related compounds known as lignocellulosic, which are mostly composed of a variety of organic polymers that can be converted into bio-oil using the HTL. The current endeavour focuses on the recent improvement in the HTL process and important parameters employed in biocrude oil production from lignocellulosic waste, and the effects of HTL conditions on the yield of bio-oil biochar composition are critically also reviewed. © 2023 John Wiley & Sons Ltd.