The aim of this study is to investigate the predictive factors that predispose secondary school students' interest in studying STEM (Science, Technology, Engineering, and Mathematics) fields in higher education. For this purpose, an already existing questionnaire was used and modified properly, according to the Greek educational system. The survey was attended by 301 secondary school students, who study in Piraeus, one of the largest cities in Greece. Research findings indicated that the principles of Social Cognitive Career Theory (SCCT) are well supported. It is worth mentioning that this is the first time that such a number of variables had been examined, in order to support the SCCT. In particular, very few studies exist in literature--to the best of our knowledge--investigating the effect of more than four factors influencing students' interest towards STEM higher studies. Learning experiences, students' exposure to STEM activities within the school environment and outside of it (OR = 0.071, p = 0.002), as well as their involvement with high difficulty STEM courses (OR = 0.203, p = 0.038), appear to be positively correlated with the development of interest towards studies in the STEM fields. In addition, students from low-income families are more likely to follow STEM studies (OR = 0.198, p = 0.034). On the contrary, it has been revealed that parental educational background only supports the student's decision to continue studies after high school, without specifying the educational field in higher education (OR = 0.769, p = 0.703; father's educational level, OR = 0.698, p = 0.552; mother's educational level). Data revealed that outcome expectations and self-efficacy (OR = 14.366, p = 0.005) are positively related to the procedure of students' interest development to pursue STEM fields in higher education, while gender seems to be a non-regulatory factor (OR = 0.886, p = 0.831).