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INTRODUCTION: Leptospirosis is typically transmitted when persons are exposed to infected animals or contaminated environments. Human-to-human transmission is currently reported non-systematically, and has unknown public health implications. METHODS: Therefore, literature searches were performed on Embase, PubMed, Scopus, and Web of Science databases to identify relevant publications. Clinical data describing the index and secondary cases were extracted and the evidence strength was assessed. RESULTS: The search yielded 10,658 results, and 27 publications covering 34 suspected reports were included. Strong evidence (n = 12) was found for vertical transmission occurring either transplacentally or via lactation. Transmission via sexual contact (n = 3) and blood transfusion (n = 1) was not well proven. DISCUSSION: Human-to-human leptospirosis transmission may play a role in leptospiral epidemiology and lead to clinical cases, especially through vertical spread. However, no evidence of sustained human-to-human transmission was found as there was no record of infections beyond the secondary cases. Public health systems in endemic areas should remain vigilant for these less-reported modes of transmission to safeguard health. Robust One Health surveillance is required to improve detection and awareness, reduce underreporting and improve disease control.