Polyethylene terephthalate (PET) fibers are the most numerous synthetic fibers in the world, but their flammability and high-temperature melt dripping limit their further applications. To address these issues, a copper porphyrin derivative, i.e., copper 2‑methoxy-4-(10,15,20-tris(4-((diphenylphosphoryl)oxy)-3-methoxyphenyl) porphyrin-5-yl) phenyl diphenylphosphinate (MTPD-Cu) was firstly synthesized from biomass vanillin in this paper. Then, MTPD-Cu was used for the surface modification of PET fibers via the dyeing process to prepare multifunctional PET fibers (FR-PET) with dyeing, flame retardant and anti-dripping properties. The flame retardancy, thermal stability, anti-dripping and color fastness of FR-PET were evaluated by limiting oxygen index (LOI), burning test, micro combustion calorimetry (MCC), thermogravimetric analyzer (TGA), and water washing color fastness test. The results revealed that the LOI value increased from 21% for pure PET fibers to 29.8% for FR-PET fibers. Meanwhile, compared to pure PET fibers, the total heat release (THR) and peak heat release rate (PHRR) of FR-PET decreased by 79.8% and 57.8%, respectively. The residual char of FR-PET was significantly improved whether in nitrogen or in air atmosphere at 800 °C, showing good char forming ability. In addition, FR-PET exhibited no melt dripping phenomenon and was pink with excellent color fastness to washing. Furthermore, the possible flame retardant and anti-dripping mechanisms were also proposed. This work provides a simple and easy modification method to simultaneously endow PET fibers with dyeing, flame retardancy and antibacterial properties, which is easy to be prepared on a large scale.