This study examines a dual-stage process for converting pine needle biochar pyrolyzed at varying temperatures (300°C, 400°C, and 500°C) into carbon nanotubes under microwave irradiation conditions and varying ferrocene-to-biochar ratios (1:1,1:2, and 1:3). The synthesized carbon nanotubes were characterized to evaluate their concentration, average diameter, crystalline structure, and degree of graphitization. The pine needle–derived carbon nanotubes synthesized from carbon precursors pyrolyzed at 500°C demonstrated the highest degree of wall graphitization, evidenced by an I<inf>D</inf>/I<inf>G</inf> ratio of 0.86. The synthesized pine needle waste–derived carbon nanotubes exhibited average diameters ranging from 65 to 97 nm with a tubular morphology similar to that of multiwalled carbon nanotubes. These pine needle–derived carbon nanotubes were further functionalized with hydroxyl groups and used as a heterogeneous catalyst in biodiesel production from waste cooking oil. Under optimum conditions of a reaction time of 102.15 min, reaction temperature of 57.5°C, methanol-to-oil molar ratio of 7.96, and catalyst loading of 1.38% wt., a maximum biodiesel conversion of 97.56% was obtained. Overall, the proposed study paves the way for sustainable utilization of waste materials such as pine needles to value-added materials and their application as heterogeneous catalysts in biodiesel production from waste cooking oil. © © 2025 Sai Parameshwar et al. Journal of Nanotechnology published by John Wiley & Sons Ltd.