Introduction Concussion-related clinical practices lack quality and consistency worldwide. The level of clinicians’ self-efficacy, a belief in ability to succeed in the context of concussion-care, might be a contributing factor. This research aimed to explore Irish clinicians’ concussion-related self-efficacy during professional education and clinical practice, through the lens of the triadic reciprocal determinism (TRD) model and the four general self-efficacy sources. Methods In total, 285 clinicians (certified athletic therapists, chartered physiotherapists, emergency medical services professionals) and 98 final-year athletic therapy (AT) students participated in a cross-sectional, quantitative evaluation of self-efficacy in concussion assessment and management skills, clinical practices and factors impacting self-efficacy. Following that, guided by an interpretative phenomenology approach, qualitative investigation of factors influencing development of self-efficacy during professional education and clinical practice took place. The perceptions of 12 clinicians and 20 AT students were investigated using a semi-structured interview/focus group format, and reflexive thematic analysis approach. Findings of the aforementioned investigations guided development of recommendations for educational practice. Results The overall levels of concussion-related self-efficacy among Irish clinicians and AT students were moderate. However, their skill-specific scores varied from very low to high and correlated with frequency of their use with concussed patients. All general sources of self-efficacy were found relevant in the context of concussion-care. Although practice in a relaxed, real-life environment and educators’ feedback were the highest-rated influencing factors, broader environmental and personal factors modified the outcomes of those experiences, in line with the TRD model. Concussion-related self-efficacy is a dynamic attribute that fluctuates throughout clinicians’ professional life. The period of enrolment on professional education programmes is critical for the development of a strong self-efficacy foundation. Conclusion Concussed patients in Ireland receive care from clinicians who feel only moderately efficacious about delivery of optimal concussion-care. Professional and personal development should be promoted throughout professional healthcare education and embraced by the students. Clinicians should strive for excellence utilising a variety of continuing professional development opportunities. However, achieving high-level concussion-related self-efficacy might not be possible without joint support of stakeholders and mentors within clinicians’ professional education and work environments.