The present thesis aimed to examine the relationships among Internal Marketing, Customer Satisfaction, and Well-Being, considering Employee Engagement as a potential mediating variable. To do so, data were from two separate populations: employees and customers of the same organization. While this was not an ideal method due to the absence of paired observations, an indirect approach was adopted, analysing internal relationships and external ones independently. The results revealed that not only do internal marketing practices emphasizing communication, recognition, and employee participation significantly predict employee engagement, but also that customer satisfaction and well-being are strongly related, suggesting that customers’ well-being can emerge even in contexts involving controversial products when relational experiences are positive. Although the mediation could not be directly tested, the consistency between the findings and previous literature supports the theoretical proposition that employee engagement serves as a mechanism that translates internal marketing practices into improved customer perceptions. The study contributes to the literature by highlighting the internal–external link between employees and consumers and suggests that organizations aiming for sustainable customer well-being should begin by investing in their internal culture and engagement strategies.