Background: With widespread adoption of the Next Generation Science Standards (NGSS) in the USA (US), research is needed on how secondary science, technology, engineering, and mathematics (STEM) teachers conceptualize the integration of engineering knowledge and practices in traditional STEM classrooms. The present study explored the affective impacts of participation in an engineering education workshop for secondary STEM teachers as part of a 200-h professional development program. The workshop focused on the implementation of electrical engineering and biotechnology principles and design practices in disciplinary instruction, as well as training teachers to differentiate among engineering fields and advise on career pathways. The conceptual framework for the workshop design was based upon elements of the interconnected model of professional growth to identify influences contributing to engineering pedagogical self-efficacy and career awareness. Results: The overarching research questions addressed how professional development in engineering education affected secondary STEM teachers' beliefs about the value of using engineering design to support learning, their self-efficacy regarding teaching engineering in their courses, perceived obstacles to effective STEM integration, and their confidence advising students about engineering post-secondary study and careers. The convergent parallel mixed methods design involved factor analysis, comparisons of means, and phenomenology with elements of grounded theory. The survey sample included 60 STEM teachers in the treatment group and 28 teachers in the control group. Six science teachers participated in interviews before and after the engineering workshops. Findings indicated that participating teachers significantly improved their confidence in engineering pedagogy, as well as their knowledge of engineering careers and precollege preparation for post-secondary engineering. Teachers expressed their views of engineering as a potentially powerful tool in developing students' critical thinking and problem-solving skills, particularly when integrating the practices of science and engineering with the instruction of disciplinary content. Conclusions: The results from this study demonstrate that a university-based professional development workshop series, developed by engineering and science education faculty, is an effective first-step intervention to improve the engineering knowledge and skills of secondary STEM educators, ultimately facilitating NGSS adoption in classroom instruction. Educating teachers on engineering career pathways is another innovation for the promotion of more diverse participation in engineering fields.