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Broadband optical absorbers are significant for applications in solar energy harvesting, thermal emitters, and infrared detection. Broadband solar absorbers should have the advantages of broad solar spectrum utilization, good thermal stability, easy large-area fabrication, polarization independence, and insensitivity to incident angle. In this work, the ultra-broadband absorption of metallic truncated nanocones in the ultraviolet–visible–near-infrared spectral region is reported. The average absorptivity in the wavelength range of 100–2500 nm is 96.11%, and greater than 96% absorptivity can be continuously maintained in the range of 160–1470 nm. The results of a finite-difference time-domain simulation using air mass 1.5 show that the metallic truncated nanocones have an average solar absorptivity of 94.22% between 280 and 2500 nm. The absorptivity in the wide oblique angle range of 0–70° along all polarizations is higher than 80%. The effect of the geometric parameters of the metallic truncated nanocones on broadband absorption is discussed. The interaction of local surface plasmonic resonance, Fabry-Perot cavity resonance, and magnetic polarization resonance in the truncated nanocones leads to the high absorption performance. The feasibility of fabricating the truncated nanocones was verified using self-assembled monolayer colloidal crystal-assisted ultraviolet light lithography followed by atomic layer deposition of platinum. The average absorptivity of 74.82% presented from photoresist and platinum arrays is close to that of the simulated data.