A novel electromagnetic-based method is presented for monitoring elemental sulfur deposition within a natural gas-carrying pipeline. The deposited sulfur behaves as a superstrate layer above a sensing microstrip patch antenna that is optimally placed on the inner wall of the gas pipeline. Increasing the superstrate thickness by the sulfur deposition alters the antenna resonance behavior, which can be monitored externally using a vector network analyzer. The effect of uneven or bumpy sulfur deposition is studied. Sensing antennas positioned outside a plexiglass pipeline are also investigated to observe the change in the antenna impedance matching with accumulating sulfur superstrate. A variation in the resonance frequency of the invasive sensing antenna from 10.14 to 8.32 GHz is observed for a deposited sulfur thickness that ranges from 0–7 mm. The sensing sensitivity is found to be 0.23 GHz/mm. Lab-based measured results agreed well with the simulated responses using commercial electromagnetic software. The proposed low-cost and easy-to-implement detection technique accurately estimates the deposited sulfur thickness inside the natural gas-carrying pipelines.