This letter reports an efficient broadband metal–semiconductor–metal (MSM) photodetector based on an Ag/Cu2MoS4 (CMS) nanosheets/Ag architecture fabricated on a SiO2-coated Si substrate. The CMS nanosheets were synthesized via a low-cost, one-pot solvothermal method. The MSM device was realized by thermal evaporation deposition of Ag electrodes onto the CMS film. The photoresponse characteristics were systematically evaluated under UV–visible illumination (385–624 nm). The device delivered optimal performance at 385 nm, achieving a responsivity of ~6.82 A/W, a detectivity of 2.05 × 1012 Jones, and an external quantum efficiency (EQE) of 2196% under an incident power density of 0.83 mW/cm2 at a 3 V bias. Additionally, the device exhibited fast temporal response under white light illumination, demonstrating rise and fall times of 180 ms and 330 ms, respectively.