Significance The DPANN superphylum is a grouping of symbiotic microorganisms categorized based on their genomic contents and a few examples of cultivation experiments. Although the genome information of DPANN archaea is increasing year by year, most of them have remained uncultivated, limiting our knowledge of these organisms. Herein, a thermoacidophilic symbiotic archaeon (ARM-1) from the DPANN superphylum was successfully cultivated and characterized. We determined its physiological, morphological, and genomic characteristics in detail and obtained experimental evidence of the symbiotic lifestyle of this archaeon. Notably, ARM-1 is a symbiotic archaeal strain that showed dependence on a range of host species in a laboratory culture. The results significantly contribute to the true understanding of the physiology and ecology of DPANN archaea.