The possibility of producing hydrogen and methane from sedimented pulp and paper mill waste fibre was explored for the first time in a double-stage process. Hydrogen and methane production was compared in batch experiments under four different conditions: two-stage hydrogen and methane production under (i) mesophilic (37 °C) and (ii) thermophilic (55 °C) and one-stage methane production under (iii) mesophilic and (iv) thermophilic conditions. Among these conditions studied, two-stage thermophilic anaerobic digestion achieved the highest hydrogen yield (42.1 ± 2.91 mL/g VS) and methane yield (334 ± 26.8 mL/g VS) at 55 °C. The experimental results were fitted to modified Gompertz equation, and a strong correlation was built from the overall magnitude of the regression (R2 ranged from 0.996to 0.989) between the experimental data and the applied equation. Total energy yield from the two-stage thermophilic process was higher (3.7 kWh/L) than the one-stage process (1.7 kWh/L). The two-stage treatment also reduced the treatment time by half. Knowledge gained from this study will provide a basis for future investigation of two-stage treatment of sedimented fibres. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.