In the interest of building a larger and more diverse science, technology, engineering, and math (STEM) workforce, many K-12 STEM programs have proliferated in recent years, yet the long-term effects of participation in these programs remain underexplored. This mixed methods study focuses on an established program, Science Olympiad, and uses administrative, survey, and focus group data to investigate characteristics of former Science Olympiad participants at one postsecondary institution and participants' perceived influence of the program on their postsecondary trajectories. Using social cognitive career theory, we identify themes in the ways in which Science Olympiad influenced academic and career decisions among participants, especially focusing on college and major choices. Among former participants who indicated that the program influenced their college decisions, participation in a state tournament hosted by the site institution was especially impactful. Half of the study participants indicated that the program influenced their major choice at this institution, largely through providing opportunities for exposure to and exploration of new subject areas with limited risk. Data suggest that Science Olympiad can influence participants' academic and career interests and trajectories, highlighting implications for K-12 STEM out-of-school programs and opportunities for enhanced partnerships between K-12 and postsecondary STEM educational settings.