Among the studies in the area of organisational performance analysis, little attention is paid to assessing the impact of employee well-being on business performance. Therefore, the aim of this study was to identify the sources of employees’ psychological well-being and assess its impact on business performance. The study was conducted in the form of a diagnostic survey among seven pharmaceutical entities operating in the market in Poland. The analysis and inference were based on the rules of economic and financial analysis, with particular emphasis on the cause–effect approach in the study of relationships. The sample of respondents was made up of seven pharmaceutical companies operating in the market in Poland, so the findings developed relate only to the companies accepted for the study and cannot be transferred to the general population of the country’s pharmaceutical sector. The objective of the study was made possible by appropriately selected methods of qualitative and quantitative nature. The study used the results of our own research (diagnostic survey), methods drawn from the instrumentarium of economic analysis (cause–effect analysis and dependency analysis) and statistical research techniques. The main findings of the paper indicate that the quality of organisational performance and its ability to shape the performance of activity-dependent firms is significantly dependent on the mental well-being of the workforce, as confirmed by the survey results. Firms with very good and good performance in operations demonstrate 88% of their staff achieving mental well-being. A key determinant of the above is job security (very important) and salary. The above leads to the fundamental conclusion that an important aspect of the management of a modern company is care for the comfort of working conditions, proper relations and determining the psychological safety and satisfaction of employees, which is unquestionably in the interest of both parties. The findings developed enrich the source material that can serve the management of organisations in shaping a sustainable HR strategy.