A flame-retardant vanillin-derived monomer, a process for forming a flame-retardant polymer, and an article of manufacture comprising a material that contains flame-retardant vanillin-derived monomer are disclosed. The flame-retardant vanillin-derived monomer can be synthesized from vanillin obtained from a bio-based source, and can have at least one phosphoryl or phosphonyl moiety with phenyl, allyl, epoxide, or propylene carbonate substituents. The process for forming the flame-retardant polymer can include reacting a vanillin derivative and a flame-retardant phosphorus-based molecule to form the flame-retardant vanillin-derived monomer, and then polymerizing the flame-retardant vanillin-derived monomer. The material in the article of manufacture can be flame-retardant, and contain the flame-retardant vanillin-derived monomer. Examples of materials that can be in the article of manufacture can include resins, plastics, adhesives, polymers, etc.