Vaccines have reduced the transmission and severity of COVID-19 but there remains a paucity of efficacious treatment for drug resistant strains and more susceptible individuals, particularly those who mount a sub-optimal vaccine response, either due to underlying health conditions or concomitant therapies. Repurposing existing drugs is a timely, safe and scientifically robust method for treating pandemics such as COVID-19. Here, we review the pharmacology and scientific rationale for repurposing niclosamide, an anti-helminth already in human use as a treatment for COVID-19. In addition to potent antiviral activity, niclosamide has shown pleiotropic anti-inflammatory, antibacterial, bronchodilatory and anticancer effects in numerous pre-clinical and early clinical studies. The advantages and rationale for nebulised and intranasal formulations of niclosamide, which target the site of primary infection in COVID-19, are reviewed. Finally, we provide an overview of ongoing clinical trials investigating niclosamide as a promising candidate against SARS-CoV-2.