This chapter provides an overview of the most recent advances in the mechanistic study of hydrothermal carbonisation (HTC) and the strategies to improve the conversion by using carbon-based catalysts. HTC, although not a recent discovery, has lately been receiving increasingly attention by both academic and industrial sectors due to the possibility to exploit this process to perform a simple, green and inexpensive conversion of bio-derived waste material into valuable chemicals and advanced materials and, as such, this chapter will also look into the use of hydrochars formed in HTC and their application in catalysis, more specifically heterogeneous catalysis with a mention on electrocatalysis. The versatility and tuneability of these solids give rise to the great range of applicability in different fields. A detailed overview of the HTC process is presented and the main uses of hydrochars in catalysis is then shown, highlighting their use as solid acid catalysts, as pristine solid catalysts, as sacrificial agents in synthesis, since their removal through combustion is easy, and the niche application of these solids in electrocatalysis for future research perspective.