Dosimeters maximize benefits and minimize potential risks by recording patient doses during therapeutic and diagnostic procedures in medical settings. Biochar derived from coconut shell waste exhibits promising characteristics for use as a passive thermoluminescence (TL) dosimeter in clinical radiation settings. This study evaluates the dosimetric and kinetic properties of biochar irradiated with 6–20 MeV electron beams from a medical LINAC across doses of 2–20 Gy. The TL characteristics analyzed include dose linearity, sensitivity, energy dependence, fading, and reproducibility. A highly linear dose response up to 20 Gy (R2 = 0.996), verifying the materials reliability for quantitative dosimetry. Its high reproducibility (SD < 4%) and very low fading rates (~16–17% in 28 days for dark and light storage) are further evidence of its stability. More significantly, biochar demonstrated energy independence across the explored clinical electron beam energies, demonstrating its robustness for field applications. The determined minimum detectable dose (MDD) was as low as 0.3 Gy, indicating its sensitivity at clinically relevant dose ranges. Kinetic analysis revealed general-order kinetics with activation energies of 0.33–0.46 eV and stable trap dynamics, supporting reproducible dosimetric performance. These findings support the potential of biochar as a sustainable and affordable TL dosimeter for clinical electron beam applications in radiotherapy.