We developed an upcycling process of polyurethane obtaining porous nitrogen-doped carbon materials that were applied in supercapacitor electrodes. In detail, a mechanochemical solvent-free one-pot synthesis is used and combined with a thermal treatment. Polyurethane is an ideal precursor already containing nitrogen in its backbone, yielding nitrogen-doped porous carbon materials with N content values of 1–8 wt %, high specific surface area values of up to 2150 m²·g⁻¹ (at a N content of 1.6 wt %) and large pore volume values of up to 0.9 cm³·g⁻¹. The materials were tested as electrodes for supercapacitors in aqueous 1 M Li₂SO₄ electrolyte (100 F·g⁻¹), organic 1 M TEA-BF₄ (ACN, 83 F·g⁻¹) and EMIM-BF₄ (70 F·g⁻¹).