This study examined factors influencing career indecision at the time of graduation among Korean vocational high school students, as the proportion of undecided students continues to rise. Using a hierarchical generalized linear model (HGLM), this study investigated how students’ background factors, individual characteristics, and school-level educational experiences are associated with career indecision. The main findings are as follows: First, gender, parental educational attainment, parental involvement in schooling, educational aspirations, and employment-oriented enrollment motivation show significant relationships with career indecision. Second, satisfaction with school life emerges as a protective factor that reduces the likelihood of career indecision, whereas participation in career education, counseling, and employment support programs shows no statistically significant effect. Third, at the school level, higher levels of professionalism among vocational subject teachers correspond to an increased likelihood of career indecision, while positive teacher–student relationships are linked to a decreased likelihood of career indecision. Fourth, a cross-level interaction effect reveals that students with highly involved parents are more likely to experience career indecision when attending schools with highly professional vocational subject teachers. Based on these results, this study discusses implications for the role of school education in reducing career indecision during the school-to-work transition among vocational high school students.