Globally, invasive alien species (IAS) present substantial socio-economic and environmental challenges, typically forming dense thickets and stands, which are largely accessible, unexploited, and underutilised sources of biomass. Therefore, this study examines the bioenergy potential of three IAS with woody stems, Combretum malabaricum (CM), Mimosa pigra (MP), and Ipomoea carnea (IC), as sustainable raw materials for charcoal production via carbonisation. It also examines the physico-chemical and energy properties of the resulting charcoals, thus presenting a sustainable valorisation approach. Carbonisation was conducted in a muffle furnace at a temperature of 600 °C and with a 30-minute residence time, followed by charcoal characterisation. Next, the charcoals were characterised to gravimetrically and computationally determine their mass yield (MY), higher heating value (HHV), and energy yield (EY). The results revealed that IAS charcoals have promising properties based on these analyses. The MYs were 21.77%, 27.18%, and 26.65% for CM, MP, and IC, respectively. Furthermore, the HHV values were 27.16 MJ/kg, 26.65 MJ/kg, and 26.70 MJ/kg, whereas the EY values were 5.91%, 7.24%, and 7.12% for CM, MP, and IC, respectively. The HHV indicates that the charcoals synthesised from the IAS are promising alternatives to traditional tree-type sources, presenting solutions to the challenges posed by felling trees, deforestation, and biodiversity linked to charcoal production. Additionally, the results underscore the twin merits of utilising these abundant and underutilised IAS, which would contribute to weed control, environmental management, and renewable/sustainable energy generation. Future research will concentrate on the optimisation of the carbonisation parameters and product charcoals and explore specialised applications.