This study examined how on-the-job training enhances employee performance in Deposit Money Banks in Nigeria, with particular attention to the mediating role of employee competence and the moderating influence of employee tenure. The study adopted a quantitative research design and utilized data from 1,000 employees drawn from six Deposit Money Banks in Nigeria: GTB, Zenith Bank, Access Bank, United Bank for Africa (UBA), FirstBank, and Fidelity Bank. On-the-job training was measured through coaching, mentoring, job rotation, and apprenticeship, while employee performance was assessed through task performance, contextual performance, service quality ratings, and sales-target achievement. The findings revealed a strong positive relationship between on-the-job training and employee performance. A one-unit increase in the overall on-the-job training index was associated with a 0.51-unit increase in task performance (p < .001), with the model explaining approximately 33% of the variation in task performance. Coaching produced the strongest effect on employee performance (β = .28), followed by apprenticeship (β = .21), mentoring (β = .17), and job rotation (β = .12). Mediation analysis showed that approximately 54% of the effect of on-the-job training on performance operated through improved employee competence. The performance-enhancing effect of on-the-job training was approximately 1.8 times stronger among employees with less than five years of tenure. The study concludes that on-the-job training is a strategic human resource development mechanism for enhancing competence, engagement, productivity, service quality, and overall employee performance in Nigerian Deposit Money Banks.