In recent decades, the issue of environmental sustainability has become increasingly important worldwide and there is growing pressure from stakeholders for companies to transform themselves in order to mitigate their environmental impacts. Green Human Resource Management (GHRM) plays an important role in promoting a corporate culture of environmental responsibility, ensuring the effectiveness of companies’ environmental strategy through its direct role with employees. In response to the lack of studies on GHRM and its implementation in the Portuguese business context, this study aims to map the GHRM practices implemented by companies operating in Portugal and to identify the perceived benefits, constraints, and challenges in implementing these practices. A total of 15 semi-structured interviews with human resource managers and environment-related management professionals of companies selected from an Environmental Management Systems—ISO 14001 database were conducted. The results show that organizations in Portugal implement environmental practices that fall within the scope of GHRM. The practices identified also range across transversal categories such as digital, mobility, products and waste management, infrastructure, performance, production, and corporate events. However, a holistic approach is needed and GHRM should be built under a multidimensional and well-planned system. This study argues that perceived benefits are constrained by the specific characteristics of the Portuguese business context which results in obstacles for the implementation and success of GHRM practices. The implications of the results for the organizations are discussed and suggestions are put forward.