Due to their numerous advantages, such as light weight, sustainability, cost and damping capacity, plant fibre composites (PFCs) have been recently introduced into fibre metal laminates (FMLs). The present study is focused on the thermal and hydrothermal ageing of flax/polypropylene composites and their stainless steel hybrid laminates. The results show that hybridization of PFCs with thin stainless steel sheets provides a significant increase in bending and impact properties. Immersion in water at 70 ◦C induces a significant decrease in bending properties, but the bending stiffness of the laminates is still suitable for semi-structural applications. No significant influence on the impact force and energy absorption but a change in the deformation mode are observed for the considered ageing times. Thermal ageing in air at 120 ◦C induces a significant degradation in the bending and impact properties of the composites for exposure times longer than 50 days. This is mainly due to the embrittlement of the polypropylene induced by thermal oxidation.