An effective information system (IS) function depends to a great extent upon the perceived system quality, information quality, and service quality by business units across an organization. Effective IS departments ideally design IS systems, share information, and deliver services to distinct business units in organizations to assist business employees in performing their tasks, which provide the latter’s organizations with their achieved goals and valued outcomes. Focusing on better linkages between IS and business units, in which IS professionals differently help business employees with their information technology (IT) issues, develops business employees’ perception of the quality of systems, information, and services. Indeed, IS professionals provide business employees with a channel to acquaint them with different features embedded into designed systems, to develop their IT-required skills by technical information, and to facilitate their task accomplishment by timely, responsive IT services. This channel has expanded from meeting business employees’ routine needs to assisting them beyond the call of duty by displaying positive, supplementary behaviours to task-related behaviours. However, the IS literature is silent on how these behaviours can occur among IS professionals and their non-IS colleagues, and how it affects IS departments’ effectiveness, including the quality of produced systems, shared information, and delivered services from IS departments. Building on organizational citizenship behaviour (OCB) theory, we describe a set of IS-specific OCBs directed towards IS and non-IS peers by IS professionals in a multilevel model of which such behaviours occur within IS departments, and between IS departments and business units. Individual-level analyses indicate disparate IS-specific OCBs carried out by each IS professional, and suggest motivators that encourage OCBs and inhibitors that cease the occurrence of OCBs inside IS departments. Hence, we draw on team-member exchange (TMX) and leader-member exchange (LMX) theories to explain how the quality of relationships among IS professionals and between IS professionals and their IS leaders affect IS-specific OCBs within IS departments. Also, we build upon job burnout theory to examine the nature of IS job characteristics and how negative effects of IS jobs limit carrying out IS-specific OCBs within IS departments. Cross-level analyses illustrate how business employees’ perception of unit-level system, information, and service quality is determined by the levels of IS-specific OCBs each IS professional displays. Unit-level analyses show that a set of IS-specific OCBs directed by IS departments towards business units impacts on perceived unit-level system, information, and service quality. Our empirical test of the model employs data from 1112 business employees and 529 IS professionals in 32 large global banks and insurance companies. Overall, our findings suggest that the quality relationships within IS departments promote IS-specific OCBs and the levels of work exhaustion arising from the lack of autonomy, workload, role ambiguity, and role conflict restrict the levels of IS-specific OCBs. Our findings also show that IS-specific OCBs positively affect the system, information, and service quality of IS departments, and emphasize a greater impact of IS-specific OCBs on an IS department effectiveness at individual level than unit level. This study contributes to extant literature by considering IS-specific OCBs exhibited by either IS professionals or IS units and their effects on the effectiveness of IS departments that have been overlooked by most prior research. This study also extends the current literature of antecedents of IS-specific OCBs and how quality of relationships can mitigate the negative effects of endured pressures created by the nature of IS jobs. Our findings provide insights for managers to leverage and promote IS-specific OCBs within IS departments to boost the likelihood of IT contributions to business successes.