Among the many actions required to avert further intensification of today’s social, ecological and health crises is also the improvement of healthcare’s environmental sustainability, including in countries particularly vulnerable to such crises. The present study aimed to identify Namibian healthcare professionals’ knowledge, attitudes and practices, along with barriers and educational needs, as a foundation for context-relevant interventions. The study used a non-experimental, descriptive quantitative research design with an existing validated cross-sectional questionnaire as its data collection tool. Both purposive and snowball sampling were used to select healthcare professionals (n = 71) to participate in the quantitative online questionnaire. R (version 4.2.1) software was used to analyse the data from the completed questionnaires. The results showed that the Namibian healthcare professionals participating in this study have basic knowledge of and positive attitudes toward environmental sustainability in healthcare. However, various barriers to implementing strategies towards environmental sustainability exist that currently prevent the implementation of relevant practices. These should be overcome by the Namibian health system by providing the necessary frameworks, policies, measures and resources to drive improvements in environmental sustainability. Additionally, future and current healthcare professionals must receive training across all professional education levels to enable implementation in practice and effective advocacy and planetary health promotion.