Broadband absorbers generally consist of plasmonic cavities coupled to metallic resonators separated by a dielectric film, and they are vertically stacking configurations. In this work, we propose an ultra-broadband nanowire metamaterial absorber composed of an array of vertically aligned dielectric nanowires with coaxial metallic rings. The absorber shows strong absorption from 0.2 to 7 μm with an average absorption larger than 91% due to the excitation of gap surface plasmon polariton modes in Fabry–Perot-like resonators. Moreover, a refractory dielectric cladding can be added to improve the thermal stability of the absorber, showing a negligible impact on its absorption performance. The proposed absorber may find potential applications in solar energy harvesting, infrared imaging and spectroscopy, and optoelectronic devices.