<p>The integration of eco-friendly composites based on polymers and conductive fillers offers exciting opportunities for creating sustainable materials with superior electrical properties, paving the way for innovative advancements in electroanalytical devices. In this study, we explored the potential of biodegradable polylactic acid (PLA), carbon black (CB), and biochar derived from coconut shell waste to develop fused filament fabrication (FFF) filaments without the need for hazardous solvents. To assess the influence of biochar on the electrochemical properties, additional filaments composed exclusively of CB and PLA were also fabricated for comparison. The resulting conductive FFF filaments were used to fabricate additively manufactured electrodes. The biochar-CB/PLA electrode presented superior electrochemical activity, as indicated by cyclic voltammetry (CV) scans for both outer-sphere ([Ru(NH₃)₆]^2+/3+) and inner-sphere ([Fe(CN)₆]^3-/4-) redox couples. The biochar-CB/PLA electrodes also exhibited a lower charge transfer resistance (<i>Rct</i> = 1.01 ± 0.05 kΩ) than the CB/PLA sensor (<i>Rct</i> = 9.11 ± 0.03 kΩ), highlighting the improved performance of the conductive biochar-CB/PLA filament in the production of working electrodes. The biochar, acting as an adsorbent, enhances electrochemical performance by pre-concentrating analytes at the electrode surface. Furthermore, the biochar-CB/PLA electrodes were successfully employed to detect carbendazim (CBZ), a widely used fungicide, in environmental (lake and tap water) and food (lemon juice and drinking water) samples, using differential pulse voltammetry (DPV). A linear range of 0.1 to 5.0&#xa0;µmol L⁻¹ and a limit of detection (LOD) of 0.01&#xa0;µmol L⁻¹ were achieved for CBZ determination. Recovery values (~ 90–115%) were achieved for the analysis of samples, indicating the potential of biochar-CB/PLA-based electrodes for reliable and sustainable electrochemical sensing applications.</p> Graphical Abstract <p></p>