Biochar (BC) is a porous, rigid, highly stable carbonous material yielded by biomass conversion mass through pyrolysis. BC was produced by various biomasses, such as garden wastes, agricultural wastes, algae, municipal and industrial wastes, tire waste, sludges, food waste, etc., by hydrothermal carbonization, pyrolysis, and gasification. BC is an effective, innovative approach toward a circular economy. Incorporating metals/non-metals within the BC might tune the surface functionalization/modification. These modifications include altering the surface charge of BC using metal nanoparticles (NPs) and significantly improving the applicability toward end applications. Furthermore, beyond the existing research, further investigations are needed to understand how functionalized BC additives affect plant growth, microbial communities, and the environment. Therefore, future research efforts will focus on developing techniques to optimize functional BC production yield, enhance electrode supercapacitor manufacturing, mitigate agglomeration issues, and explore healthcare applications.