The gender gap in STEM (Science, Technology, Engineering, and Mathematics) is among the widest across education and professional fields, with an underrepresentation of girls and women, particularly in engineering and biomechanics. This issue begins early in education and worsens as females progress into more senior roles. To address this gap, we designed and implemented the Biomechanics Research and Innovation Challenge (BRInC), a 100-day STEM program focused on mentoring and role modelling to engage high school girls and early-career biomechanists at key phases where they most commonly disengage in STEM. We evaluated the influence of the program on (i) identity and perceptions towards science, engineering, and biomechanics; (ii) attitudes towards biomechanics, maths and science; and (iii) attitudes towards gender bias, education and career aspirations in STEM, within high school girls following participation in the BRInC program. We observed significant and positive shifts in girls’ perceptions of both biomechanics and engineering. Participation in the program appeared to lead to favourable shifts in attitudes towards biomechanics, maths, and science and fostered a positive influence on girls’ education and career aspirations, igniting an interest in future research opportunities. Innovative STEM engagement programs, such as BRInC, highlight the promising potential of targeted and bespoke approaches to address the underrepresentation of females in biomechanics and STEM-related education and careers. Future programs should strive to enhance socioeconomic and cultural diversity, employ whole of life-cycle approaches by offering programs for girls and women at various phases of the STEM pathway, and prioritize impact assessments to effectively monitor progress.