The antimicrobial resistance crisis (AMR) is associated with millions of deaths and undermines the franchise of medicine. Of particular concern is the threat of bioweapons, exemplified by anthrax. Introduction of novel antibiotics helps mitigate AMR, but does not address the threat of bioweapons with engineered resistance. We reasoned that teixobactin, an antibiotic with no detectable resistance, is uniquely suited to address the challenge of weaponized anthrax. Teixobactinbinds to immutable targets, precursors of cell wall polymers. Here we show that teixobactinis highly efficacious in a rabbit model of inhalation anthrax. Inhaling spores of Bacillus anthracis causes overwhelming morbidity and mortality. Treating rabbits with teixobactinafter the onset of disease rapidly eliminates the pathogen from blood and tissues, normalizes body temperature, and prevents tissue damage. Teixobactinassembles into an irreversible supramolecular structure of the surface of B. anthracis membrane, likely contributing to its unusually high potency against anthrax. Antibiotics evading resistance provide a rational solution to both AMR and engineered bioweapons.