Competency is important for professionals' effective performance and career development. However, little is known about the necessary competencies and proficiency in these for Thai safety officers. Therefore, this study aimed to identify the necessary competencies for this group and to compare proficiency in each competency between senior and junior safety officers. A descriptive, cross-sectional study was conducted among 73 safety officers using a self-administered questionnaire. Twenty-five competencies were classified as necessary. Mean proficiency scores were higher for senior safety officers than for more junior safety officers for all examined competencies; however, this difference was not statistically significant for 'first aid' or for 'air sampling and analytical methods'. Regulatory compliance was assessed as the most important competency. Gaps between necessity and proficiency were observed in managing safety programs for the junior group. In both groups, proficiency was lowest in the competency of mental health. The results indicate that Thai safety officers' training needs may be particularly high for regulatory compliance, managing safety programs, and mental health. Lifelong learning is important for enabling occupational safety and health practitioners to fulfill current requirements in Thailand and elsewhere. Multiple training approaches and a specialist qualification program may encourage competency development, especially for junior practitioners.