Nitazoxanide (Alinia(®)), a nitro-thiazolyl antiparasitic drug, kills diverse microorganisms by unknown mechanisms. Here we identified two actions of nitazoxanide against Mycobacterium tuberculosis (Mtb): disruption of Mtb's membrane potential and pH homeostasis. Both actions were shared by a structurally related anti-mycobacterial compound, niclosamide. Reactive nitrogen intermediates were reported to synergize with nitazoxanide and its deacetylated derivative tizoxanide in killing Mtb. Herein, however, we could not attribute this to increased uptake of nitazoxanide or tizoxanide as monitored by targeted metabolomics, nor to increased impact of nitazoxanide on Mtb's membrane potential or intrabacterial pH. Thus, further mechanisms of action of nitazoxanide or tizoxanide may await discovery. The multiple mechanisms of action may contribute to Mtb's ultra-low frequency of resistance against nitazoxanide.