<p>The <i>Nairoviridae</i> family of segmented negative-sense RNA viruses includes the serious human pathogen Crimean-Congo haemorrhagic fever virus (CCHFV), associated with a case/fatality rate of up to 40% for which no approved vaccines or treatments exist. Nairoviruses internalize via endocytosis and pass through the endolysosomal network, exploiting the changing ionic environment to promote envelope fusion. Fusion is influenced by hydrogen (H⁺) and potassium ions (K⁺), which increase in concentration as endosomes mature, regulated by host ion channels. Using the model nairovirus Hazara virus (HAZV) of the CCHFV serogroup, we performed an siRNA screen to identify cellular ion channels involved in nairovirus infection. Most high-ranking hits belonged to K⁺ and calcium (Ca²⁺) channel families. Consistent with this, we showed that clinically-approved K⁺ channel blockers quinidine, quinine and dronedarone and clinically-approved Ca²⁺ channel blockers tetrandrine and nifedipine significantly reduced HAZV activities. To further probe the role of K⁺ in HAZV infection, we used time-of-addition studies, showing K⁺ was required during entry. Biochemical experiments showed K⁺ expanded the pH range that promoted entry, potentially allowing endosome escape deeper within the endolysosomal network. These results show clinically-approved channel blockers effectively inhibit HAZV replication, suggesting repurposing existing therapies may represent promising avenues to block nairovirus infection.</p>