The construction industry plays a vital role in the economic development of the Philippines; however, it faces increasing pressure to adopt sustainable practices that balance economic, environmental, and social responsibilities. This study examined the effects of Transformational Leadership, Organizational Integrity, and Collectivism on Corporate Sustainability in medium-sized construction companies in the CALABARZON region, with Training and Development as a mediating variable. Grounded in the Triple Bottom Line and Environmental, Social, and Governance (ESG) frameworks, the study aimed to determine both the direct and indirect relationships among the variables. A descriptive-correlational research design was employed using a self-administered survey questionnaire distributed to 120 respondents, including managers, engineers, supervisors, and administrative personnel. Data were analyzed using descriptive statistics, simple regression analysis, and mediation analysis through Jamovi. Results revealed that all independent variables–Transformational Leadership, Organizational Integrity, and Collectivism–significantly influence Corporate Sustainability. Among these, Organizational Integrity emerged as the strongest predictor, followed by Collectivism and Transformational Leadership. Furthermore, Training and Development was found to significantly mediate the relationships examined, with full mediation observed for Transformational Leadership and Organizational Integrity, and partial mediation for Collectivism. The findings highlight that leadership behavior, ethical practices, and a collaborative culture are critical drivers of sustainability outcomes in construction firms. Moreover, Training and Development serves as a key mechanism in translating organizational values into effective sustainability practices. The study concludes that a holistic integration of leadership, integrity, collectivism, and continuous employee development is essential for achieving long-term corporate sustainability. These results provide both theoretical contributions and practical implications for enhancing sustainability strategies in medium-sized construction companies.