Decision making is widely considered as a fundamental organizational activity that comprises a series of knowledge management tasks. Admitting that the quality of a decision depends on the quality of the knowledge used to make it, it has been widely argued that the enhancement of the decision making efficiency and effectiveness is strongly related to the appropriate exploitation of all possible organizational knowledge resources. Taking the above remarks into account, this PhD thesis presents a human-centred, multidisciplinary approach for the integration of Group Decision Support and Organizational Knowledge Management Systems. Towards this end, a conceptual framework that properly interweaves concepts, theories and practices from the Knowledge Management, Argumentation Theory, Decision Making and Multicriteria Decision Aid disciplines is first introduced. Acknowledging that in collaborative settings the decision makers & active participation in the knowledge sharing processes is of major importance, the proposed approach also introduces a framework for the leveraging of their participation in the related processes. Furthermore, in order to functionally integrate the decision support and knowledge management processes, a software tool that fully supports the above two frameworks was developed. The core component of the proposed tool is a Discourse Graph that serves the visualization of the argumentative discourses taking place between the involved parties. In order to better support decision making, these discourses are structured and evaluated according to a set of commonly accepted Decision Making Frameworks and a set of Scoring Mechanisms that comply with broadly used Multicriteria Decision Aid models and techniques. Being based on a well-defined ontology model, the proposed approach enables the members of a group to collaborate and accomplish a common understanding. Furthermore, it facilitates the capturing of the organizational knowledge in order to augment teamwork in terms of knowledge acquisition, elicitation, processing, storage and sharing, thus further enhancing the decision making quality.