Transformational leadership and culture are identified as providing a ground for long-term organizational success during organizational changes. In literature, corporate culture and leadership come up as major factors in success of organizational transformation process in mergers and acquisitions as they have great influence on organizational structures, processes and hence performance of companies. In this context, this study aims to find out the organizational cultural and leadership characteristics of a high-tech telecommunication company in Turkey, that had been successful in protecting its competitive position and business performance despite the challenges of cultural and organizational change that are brought by a acquisition phase. In the research, elements of leadership and culture have been identified with relevance to transformational leadership and culture through surveys conducted within the company; they're described in detail considering advantages and disadvantages of such elements during organizational restructuring. This case study points out that transformational culture and transformational leadership stand as critical strengths for achieving the desired business performance during major organizational changes such as merger and acquisitions.