The frequent world changes raised by globalization, new technology development, and the increase in migration movements have generated an immensely diversified workforce. To face these challenges, managers started to seek the best strategies to effectively run this mixed environment and implement the leading diversity management policies for human resource management sustainability, which is also considered as very constructive in boosting employees’ performance, motivation, satisfaction, as well as their work engagement. Consistently, this paper examines the impact of service companies’ diversity management systems on employees’ engagement and the moderating role of organizational trust and job insecurity in that relationship. As we opted for a quantitative study, we managed a survey based on a questionnaire dedicated to 580 employees working in Hungarian companies, specializing in Marketing, Management consulting, IT, and logistics services, to effectively assess the hypothesis concluded from the literature review. With the use of structural equation modeling (SEM) as a data analysis tool, our findings reveal that diversity management has a positive significant effect on Employees’ engagement and that organizational trust and job insecurity truly and significantly mediate that association. Along with social exchange theory, our research contributes to affirming that by implementing proper diversity management practices and by ensuring a trustworthy environment and outstanding work conditions, managers are constructively able to assist their employees, raise their involvement, and minimize the level of job insecurities.