A flame-retardant aconitic acid-derived small molecule, a process for forming a flame-retardant polymer, and an article of manufacture comprising a material that contains a flame-retardant aconitic acid-derived small molecule are disclosed. The flame-retardant aconitic acid-derived small molecule can be synthesized from aconitic acid obtained from a bio-based source, and can have at least one phosphoryl or phosphonyl moiety with phenyl, allyl, or thioether substituents. The process for forming the flame-retardant polymer can include reacting an aconitic acid derivative with a flame-retardant phosphorus-based molecule to form a flame-retardant aconitic acid-derived small molecule, and combining the flame-retardant aconitic acid-derived small molecule with a polymer. The material in the article of manufacture can be a resin, adhesive, polymer, etc.