This study investigated the effect of gender stereotyping on career choices among girls in secondary schools in Uganda, with St. John's High School Mukono as the primary case study. In a national context where gendered educational and occupational sorting continued to concentrate women in lower-paying and lower-status career fields despite decades of gender mainstreaming policy, understanding the micro-level social mechanisms through which gender stereotypes shaped girls' career aspirations and choices was both theoretically important and practically urgent. Drawing on a cross-sectional survey of 218 female students from Senior Two to Senior Six, supplemented by focus group discussions and key informant interviews with teachers, guidance counsellors, and parents, the study examined how teacher gender biases, peer gender norms, parental gender expectations, and media-reinforced stereotypes influenced girls' career aspirations, subject choice decisions, and occupational self-efficacy beliefs. Descriptive statistics revealed that all four stereotyping dimensions were perceived as moderately to highly influential by respondents (means 3.34–3.81). Pearson's correlation showed significant negative relationships between gender stereotyping intensity and career aspiration breadth (r = -0.584 to -0.721, p < .001). Multiple linear regression demonstrated that the four stereotyping dimensions collectively explained 64.2% of the variance in girls' career aspiration breadth (R² = 0.642, F = 38.14, p < .001), with teacher gender bias emerging as the strongest predictor (β = -0.412, p < .001). The study concluded that gender stereotyping significantly constrained girls' career choices and recommended teacher gender sensitisation, career guidance reform, and family engagement programming as priority interventions.