Street vending constitutes a significant segment of the informal economy in India by generating employment opportunities and ensuring access to affordable goods and services for urban and semi-urban populations. Despite their substantial contribution to local economies, street vendors continue to experience livelihood insecurity arising from limited institutional support, inadequate infrastructure, restricted access to formal credit, and weak social protection mechanisms. This study examines the socio-economic determinants of livelihood security among street vendors in Paramathi Velur Taluk of Namakkal District, Tamil Nadu. The study is based on primary data collected from 355 street vendors using a structured questionnaire covering demographic characteristics, business profile, income, expenditure, access to financial services, registration status, and workplace conditions. The findings indicate that women constitute the majority of vendors, reflecting the growing participation of female workers in the informal economy. Most respondents belong to economically productive age groups but possess relatively low levels of formal education. A substantial proportion operate without official registration or vendor identity cards, limiting their access to government welfare schemes and institutional credit. Vegetable vending represents the dominant economic activity, while inadequate infrastructure, market uncertainty, and regulatory constraints continue to affect livelihood outcomes. The study concludes that livelihood security is shaped by a combination of socio-economic characteristics, business conditions, and institutional support. Strengthening vendor registration, expanding financial inclusion, improving market infrastructure, and enhancing awareness of welfare schemes would contribute significantly to sustainable livelihoods among street vendors.