Background: In Soroti City, Uganda, secondary schoolgirls increasingly engage in transactional sex as a survival mechanism to meet basic needs and educational expenses, yet the prevalence, drivers, and educational consequences of this phenomenon remain inadequately documented. Objective: This study analyzed survival sex among secondary schoolgirls in Soroti City and examined its impact on educational participation, performance, and completion. Methods: A convergent parallel mixed-methods design was employed across ten purposively selected secondary schools in Soroti City. The study involved 384 schoolgirls (aged 14-19 years) selected through stratified random sampling who completed structured questionnaires, and 15 key informants who participated in in-depth interviews, alongside 8 focus group discussions. Quantitative data were analyzed using STATA 16, employing univariate analysis (frequencies, percentages, means), bivariate analysis (chi-square tests, t-tests), and multivariable regression models (logistic regression for predictors of transactional sex engagement; linear regression for academic performance determinants). Qualitative data were transcribed and analyzed thematically using NVivo 12. Ethical approval was obtained from Makerere University, with informed consent secured from all participants and parental consent for minors. Results: The prevalence of transactional sex among secondary schoolgirls was 42.4% (n=163). Bivariate analyses revealed significant associations between engagement and age (χ²=24.67, p