Bio-based rigid diols are key building blocks in the development and preparation of high-performance bioplastics with improved thermal and dimensional stabilities. Here, we report on the straightforward two-step synthesis of a diol with a spirocyclic acetal structure, starting from bio-based vanillin and pentaerythritol. According to a preliminary life cycle assessment (LCA), the greenhouse gas emissions of this bio-based diol are significantly lower than those of bio-based 1,3-propanediol. Copolymerization of the rigid spiro-diol with 1,6-hexanediol and dimethyl terephthalate by melt polymerization yielded a series of copolyesters, which showed improved glass transition temperature and thermal stability upon the incorporation of the spiroacetal units. The crystallinity and melting point of copolyesters decreased with increasing content of the spirocyclic backbone structures. The copolyester containing 10% of the new diol was semicrystalline, while those with 20 and 30% spiro-diol incorporated were completely amorphous. Moreover, dynamic mechanical analysis indicated that the copolyesters showed storage moduli comparable to Akestra, a commercial fossil-based high-performance polyester.