A novel, entirely bio-derived polylactide carbohydrate copolymer (RP1) is used as a compatibilizer, to produce bacterial cellulose (BC) poly(l-lactide) (PLLA) nanocomposites with improved mechanical properties. Contact angle measurements of RP1 droplets on single BC nanofibres proved that it has a higher affinity towards BC than PLLA. RP1 has a comparable Young’s modulus, but lower tensile strength, than PLLA. When RP1 was blended with PLLA at a concentration of 5 wt%, the tensile modulus and strength of the resulting polymer blend decreased from 4.08 GPa and 63.1, respectively, for PLLA to 3.75 GPa and 56.1 MPa. A composite of BC and PLLA (with 5 wt% RP1 and 5 wt% BC) has a higher Young’s modulus and tensile strength, compared to either pure PLLA or PLLA–BC nanocomposites.