In this Letter, we propose a metasurface for microwave-infrared (MW-IR) co-aperture detection, which presents the advantages of low-profile, light-weight, and low cost for a facilitated integration compared to conventional MW-IR co-aperture devices. In the microwave domain, based on impedance matching, a polarization-insensitive transparent window at Ka band is achieved, and in the infrared domain, focusing is realized through a metalens by judiciously designing the diameter of the nanopillars to modulate the phase distribution at a wavelength of 9.68 μ m. To validate the co-aperture design framework, a proof-of-concept metasurface prototype is fabricated and experimentally tested. The measured results demonstrate good agreement with simulations, validating an innovative approach for MW-IR hybrid sensing, which may have potential applications in target detection, autonomous vehicles, and smart homes.