In the restaurant industry, where service quality depends heavily on skilled personnel, retaining loyal employees is a strategic priority, yet the loyalty of chefs—who function as knowledge workers—remains underexplored. Drawing on Social Exchange Theory and the Stimulus–Organism–Response framework, this study examines how internal marketing shapes employee loyalty among chefs in Iranian luxury restaurants and whether affective commitment mediates this relationship. Using a total-population sampling approach, all 400 eligible chefs in the sampling frame were invited, and 385 returned complete and usable questionnaires, which were analysed through structural equation modelling (SEM) with AMOS. The results showed that internal marketing had a significant positive total effect on employee loyalty and a significant positive effect on affective commitment, which in turn positively affected loyalty. The indirect effect of internal marketing on loyalty through affective commitment was significant, whereas the direct effect became non-significant once affective commitment was included in the model, indicating full mediation. The study contributes to the internal marketing and hospitality literature by conceptualizing chefs as knowledge workers and revealing the psychological mechanism through which internal marketing strengthens their loyalty in the underexplored context of Iranian luxury restaurants.