AbstractA novel lightwave‐driven detector that combines photomultiplier tube (PMT) technology with structured metasurfaces is presented to enable efficient detection of long‐wavelength radiation in the mid‐infrared (mid‐IR) to terahertz (THz) range. This overcomes the limitations of conventional PMT technology, which cannot efficiently detect wavelengths longer than 1.7 m. The approach utilizes the long‐wavelength radiation's instantaneous electric field to facilitate field‐driven electron emission from metasurfaces, which allows it to cover the entire THz to mid‐IR range by geometric scaling. This enables a novel class of lightwave‐driven detectors with the benefits and performance characteristics known from the established PMT technology, such as fast response times and low noise, while expanding the operational wavelength range vastly. It is shown that the amount of field‐emitted electrons depends on the THz electric field in a highly nonlinear manner, generally following the Fowler–Nordheim relation. Furthermore, the THz‐PMT can determine specific lightwave characteristics of the incident field, including its peak field strength and absolute polarity, due to its sensitivity to the sign of the electric field. With a field sensitivity as low as a few kV cm⁻¹, the THz‐PMTs provide a versatile tool for high sensitivity detection across various fields of interest in science and technology.