Highly flexible strain sensors based on graphene aerogels (GAs) have been widely researched. However, most GAs are often found to be extremely weak and delicate to handle due to the π–π stacking and van der Waals interactions between adjacent graphene sheets that lead to a brittle skeleton. Thus constructing graphene structures with excellent mechanical properties, high sensitivity and effective conductive networks is still a big challenge. In this work, we fabricate a bio-based graphene/sodium alginate aerogel with high porosity (99.61%) and low density (6–7 mg cm⁻³) via freeze drying and chemical reduction. The resulting aerogels exhibit outstanding durability (>6000 loading–unloading cycles), excellent sensitivity to compression (gauge factor is 1.01) and bending (bending sensitivity is 0.172 rad⁻¹). The strong hydrogen bonding interactions between graphene and SA are responsible for the synergetic enhancement of strength and elasticity. Taking advantage of the combination of the electronic conductivity and mechanical flexibility, the proposed bio-based aerogels may be a robust candidate in flexible strain sensors.