Proactivity is a particularly important attribute of knowledge-intensive companies, where work that requires enhancing the potential of knowledge-intensive employees in a sustainable working environment is crucial. Another important challenge for these firms is to account for the increasing importance of the functioning of the cognitive mechanisms leading to the increased well-being of knowledge workers following the implementation of a psychological contract. The aim of this article is to identify the relationship between inclusive leadership, the fulfilment of a psychological contract, two dimensions of well-being (workplace and life-related well-being), and knowledge workers’ proactivity. Based on survey data collected using the CAWI method from 1000 knowledge workers employed in Polish companies in the business services sector, the research hypotheses proposed in this study were tested using a stepwise equation-modelling (SEM) technique, which resulted in a model containing all the main constructs. The results obtained indicate that inclusive leadership positively relates to the fulfilment of the psychological contract. Furthermore, the fulfilment of the psychological contract positively associates proactive working behavior with the wellbeing of knowledge workers. Along with proactive work behavior, two dimensions of well-being were examined as outcome variables. Our analysis also shows that knowledge-intensive organizations, intending to develop the proactivity of their employees and nurture a high level of well-being in their lives and in the workplace, should ensure that they fulfil the expectations and obligations of the psychological contract. One way to achieve this is for managers to employ an inclusive management style, which supports an atmosphere of a safe working environment in a diverse setting and allows employees to feel comfortable sharing their opinions and ideas. The study of inclusive leadership in the context of knowledge-intensive organizations provides human resource professionals and employee managers with important insights into how inclusive leadership can effectively contribute to the psychological contract, which, consequently, will lead to proactive work behavior and improve employees’ workplace and life-related well-being.