INTRODUCTION: The number of lifetime sexual partners is a critical factor in public health, influencing the transmission of sexually transmitted infections and HIV/AIDS. This study aims to explore the distribution, determinants, and geographical mapping of lifetime sexual partners among three generational cohorts in India-Generation X, Generation Y/ Millennials, and Generation Z-using data from the National Family Health Survey (NFHS-5). METHODS: Data were analysed from 149,665 participants (67,352 men and 80,313 women) from the NFHS-5 (2019-2021). Participants were categorized into Generation X (born 1981-1996), Millennials (born 1997-2010), and Generation Z (born 2010-2024). The primary outcome was the total number of lifetime sexual partners, with explanatory variables including demographic, socioeconomic, health-related, and behavioural factors. Hierarchical linear regression models were employed to assess associations and generate geographical mapping across Indian states and union territories. RESULTS: The mean number of lifetime sexual partners was higher in males (3.29) compared to females (2.40), with significant regional and generational variations. Males in the North-East regions reported the highest averages, particularly among Generation X. Significant determinants included religion, caste, employment status, and health insurance. Risky behaviours, such as smoking and alcohol consumption, were positively associated with the number of sexual partners in males, while comprehensive HIV/AIDS knowledge was linked to fewer partners across genders. CONCLUSION: This study highlights significant generational, gender, and regional disparities in sexual behaviour across India. The findings suggest the need for targeted public health interventions that address specific cultural and socioeconomic contexts, promote health awareness, and integrate sexual health education with broader efforts to reduce risky behaviours and gender-based violence.