Porphyrins are unique tetrapyrrolic pigments involved in important metabolic processes in a living organism. The level of porphyrin molecules can be used as diagnostic test of the condition of the organism. At the same time, their spectral-luminescent properties make it possible to use porphyrins as potential candidates for therapy of different diseases. Here, based on the results of our studies as well as literature information, we focus on the possibility of using porphyrins (hemoglobin, bilirubin and metal-free porphyrins: proto-, copro-, uroporphyrin) as theranostic agents. The following applications of theranostics were investigated: phototherapy for neonatal hyperbilirubinemia (jaundice), photodynamic therapy of tumors, antimicrobial photodynamic therapy based on sensitizing effect of endogenous and exogenous porphyrins, and photobiomodulation (laser therapy). The excitation of exogenous and endogenous porphyrins by light induces the cascade of reactions leading to a pronounced therapeutic effect. The possible mechanisms involve formation of reactive oxygen species, which, depending on their concentration, are capable of acting as inhibiting or stimulating factor. The data show that porphyrins may also be used as potential photosensitizers for the treatment of SARS-CoV-2 patients. The data presented indicate that endogenous and exogenous tetrapyrroles are capable of acting as primary targets responsible for the therapeutic effect of light in the treatment of a wide range of diseases of various origins. On the other hand, the porphyrins can function as agents of theranostics. It allows taking into account the individual characteristics of the organism during phototherapy, controlling its response to the effect of a physical factor.