A novel photoelectrochemical (PEC) and electrochemiluminescence (ECL) bifunctional aptasensor has been established for the detection of miRNA-126 using V₂CT_x MXene-derived porphyrin-based metal–organic framework embedded with Ag nanoparticles (Ag NPs) (denoted as AgNPs@V-PMOF) as a robust bioplatform. Due to the presence of V nodes in V₂CT_x MXene nanosheets, V-based MOF was prepared using tetrakis(4-carboxyphenyl)porphyrin as ligand, followed by the incorporation of Ag⁺ ions to form the AgNPs@V-PMOF Schottky heterojunction. Benefiting from the fast electron transfer of the V₂CT_x substrate and well-matched band-edge energy level of the photosensitive Ag NPs and V-PMOF, the constructed AgNPs@V-PMOF Schottky heterojunction exhibited the promoted transfer of the photogenerated carriers, showing superior PEC and ECL performances. Moreover, a large number of the complementary DNA strand of miRNA-126 can be immobilized over AgNPs@V-PMOF in view of the combined interaction of π–π stacking, van der Waals force, and Ag–N coordination between AgNPs@V-PMOF. Consequently, the developed AgNPs@V-PMOF-based aptasensor illustrated extremely low detection limits of 0.78 and 0.53 fM within a wide range from 1.0 fM to 1.0 nM of miRNA-126 detected by PEC and ECL techniques, respectively, superior to most reported miRNA aptasensors. Also, the provided bifunctional aptasensor demonstrated high selectivity, good stability, fine reproducibility, and acceptable regenerability, as well as promising potential for the analysis of miRNA-126 from living cancer cells. This work puts forward the development of aptasensors for the early and accurate diagnosis of cancer markers and extends the application of MOF in the biosensing field.