Background: The role of career interventions and their impact on students' sense of self and preparation for careers in STEM fields is an underexplored teaching and research area within STEM education. Purpose: The purpose of our mixed-methods study was to examine how a life sciences career exploration course at a large public research university in the United States fostered undergraduates' STEM confidence and career self-efficacy. Guided by a STEM persistence framework, we also sought to establish the analytical value of including a career exploration course to the toolbox of practices, including early research experiences, active learning, and learning communities, that drive increased STEM confidence and motivation. Sample: Our study drew on a select sample of final course portfolios (N = 25) and pre-course and post-course survey data (N = 429). Design and methods: We utilized a mixed-methods approach and employed both quantitative and qualitative data analysis to demonstrate how a highly-structured and deliberate pedagogical approach to STEM career exploration increased students' satisfaction with their choice of career path, confidence in staying in their major, confidence in their ability to obtain a job and/or apply to graduate school, and their career self-efficacy. Results: The results indicated that students benefited from exposure to diverse career pathways and opportunities to practice the skills needed for conducting career research and making career decisions. Conclusion: We find that the structured career course we investigated in this study can serve as a model for institutions interested in offering a large-enrolment STEM career exploration course to provide students effective STEM career advice as well as aid in their development as a STEM-capable workforce.