Huge amount of technical lignin is produced in paper and pulp industries annually. In this article, lignin hydrothermal liquefaction (HTL) was conducted in the presence of zero valent metals (ZVMs): Zn, Fe, Ni and Co and metal-supported Al₂O₃ catalysts (Ni/Al₂O₃, Fe/Al₂O₃, Co/Al₂O₃ and Cu/Al₂O₃) in order to investigate the possibility to valorize this waste. The bio-crude yields of lignin HTL at 330 °C for 60 min were 32.2% Fe > 29.8% Ni > 28.6% Zn > 26.5% blank >25.4% Co. Fe and Zn act as hydrogen producer being oxidized by subcritical water; the hydrogen stabilized the lignin HTL intermediates, enhancing bio-crude yields which were further improved when Fe and Zn are combined with hydrogenation catalyst Ni/Al₂O₃ inducing an even higher bio-crude yield of 36.0 and 36.1%, respectively. The energy recovery of Fe + Ni/Al₂O₃ and Zn + Ni/Al₂O₃ tests reached 67.8% and 66.3%, significantly higher than 47.4% of blank test. Both ZVMs and metal-supported Al₂O₃ catalysts showed good demethoxylation function. Zn/Fe and water reaction environment was demonstrated to be promising substitution of high pressure gaseous hydrogen for lignin waste liquefaction process.