Solution-processable, single-crystalline perovskite nanowires are ideal candidates for developing low-cost photodetectors, but their detectivities are limited due to a high level of unintentional defects. Through the surface-initiated solution-growth method, we fabricated high-quality, single-crystalline, defects-suppressed MAPbI3 nanowires, which possess atomically smooth side surfaces with a surface roughness of 0.27 nm, corresponding to a carrier lifetime of 112.9 ns. By forming ohmic MAPbI3/Au contacts through the dry contact method, high-performance metal–semiconductor–metal photodetectors have been demonstrated with a record large linear dynamic range of 157 dB along with a record high detectivity of 1.2×1014Jones at an illumination power density of 5.5nW/cm2. Such superior photodetector performance metrics are attributed to, first, the defects-suppressed property of the as-grown MAPbI3 nanowires, which leads to a quite low noise current in the dark, and second, the ohmic contact between MAPbI3 and Au interfaces, which gives rise to an improved responsivity compared with the Schottky contact counterpart. The realized high-performance MAPbI3 nanowire photodetector advances the development of low-cost photodetectors and has potential applications in weak-signal photodetection.