LaFeO₃ nanospheres with an orthorhombic perovskite structure were synthesized by a sol–gel autocombustion method in the presence of different citric acid ratios (x = 2, 4, 8, and 16) and utilized for the photocatalytic conversion of o-aminophenol (OAP) to 2-aminophenoxazine-3-one (APX) for the first time. OAP is one of the most toxic phenolic derivatives used as a starting material in many industries; however, the dimerization product APX has diverse therapeutic properties. Photocatalytic conversion was carried out in ethanol/water and acetonitrile/water mixtures in the absence and presence of molecular oxygen at ambient temperature via the oxidative coupling reaction that mimics phenoxazinone synthase-like activity. The LaFeO₃ samples showed a superior photocatalytic activity of OAP to APX with rate constants of 0.43 and 0.92 min⁻¹ in the absence and presence of molecular oxygen, respectively. Thus, the LaFeO₃ nanozymes could be used as promising candidates in industrial water treatment and phenoxazinone synthase-like activity.