Nanoplasmonic hydrogen sensors are predicted to play a key role in safety systems of the emerging hydrogen economy. Pd nanoparticles are the active material of choice for sensor prototype development due to their ability to form a hydride at ambient conditions, which creates the optical contrast. Here, we introduce plasmonic hydrogen sensors made from a thermoplastic nanocomposite material, that is, a bulk material that can be molded with standard plastic processing techniques, such as extrusion and three-dimensional (3D) printing, while at the same time being functionalized at the nanoscale. Specifically, our plasmonic plastic is composed of hydrogen-sensitive and plasmonically active Pd nanocubes mixed with a poly(methyl methacrylate) matrix, and we optimize it by characterization from the atomic to the macroscopic level. We demonstrate melt-processed deactivation-resistant plasmonic hydrogen sensors, which retain full functionality even after 50 weeks. From a wider perspective, we advertise plasmonic plastic nanocomposite materials for application in a multitude of active plasmonic technologies since they provide efficient scalable processing and almost endless functional material design opportunities via tailored polymer–colloidal nanocrystal combinations.