Networked structures of percolated silver nanowires (AgNWs) are an important substitute for brittle indium tin oxide (ITO)-based transparent electrodes, owing to their high ductility and tunable optical and electrical conductivities. Recently, AgNWs have been used in the fabrication of flexible transparent heaters, but only when firmly adhered to the underlying polymer substrate so that the electrodes are reliably flexible. Another requirement is that these electrodes must be passivated from the atmosphere, preserving them even when the fabricated heaters are biased at high voltages or exposed to harsh environments. Here, we used conventional photolithography with a coating of commercial photoresist, UV exposure and development, in order to make protected AgNW networks. For this, AgNW networks preformed on a transparent polymer were used as a photomask layer, so that the photoresist could be developed to be selectively present on the AgNWs. As a result of this simple approach, the mechanical/thermal stability and heating performance of our AgNWs-based transparent heaters were successfully enhanced. It displays an increase of <2% in Rs when bent to a radius of 500 μm for 10,000 cycles, and a biasing voltage to the heater rapidly increased its temperature above 160 °C within a very short time period.