This study aimed to investigate the effects of Jiangsu University teachers' competency and engagement on their job performance and determine whether teacher competency affects job performance through the mediating role of engagement. We constructed a theoretical model based on self-determination theory (SDT) and the job demand-resource model and validated it using structural equation modeling (SEM). The study sample comprised teachers from 8 types of undergraduate colleges and universities in Jiangsu Province, China. Three hundred and fifty-four university teachers were surveyed using the Teacher Competency Scale, the Utrecht Work Engagement Scale, and the Job Performance Scale. The results showed a significant positive effect of university teachers' competency on their engagement and job performance. Additionally, SEM analysis showed a partial mediation effect of engagement in the relationship between teacher competency and job performance. The findings not only enrich our understanding of the mechanisms underlying the relationship between university teachers' competency and job performance but also extend the scope of SDT and suggest practical discussions and recommendations.