BACKGROUND: Effective leadership and change management are thought to contribute to the successful implementation of health information technology innovations. However, limited attention has been paid to the role of frontline leaders in building health professional support for new technical innovations. OBJECTIVE: First, we examined whether frontline leaders' positive expectations of a patient portal and perceptions of its implementation were associated with their support for the portal. Second, we explored whether leaders' positive perceptions influenced the same unit's health professional support for the portal. METHODS: Data were collected through an online survey of 2067 health professionals and 401 frontline leaders working in 44 units from 14 health organizations in Finland. The participating organizations run a joint self-care and digital value services project developing a new patient portal for self-management. The survey was conducted before the piloting and implementation of the patient portal. RESULTS: The frontline leaders' perception of vision clarity had the strongest association with their own support for the portal (ß=.40, P<.001). Results also showed an association between leaders' view of organizational readiness and their support (ß=.15, P=.04). The leaders' positive perceptions of the quality of informing about the patient portal was associated with both leaders' own (ß=.16, P=.02) and subordinate health professionals' support for the portal (ß=.08, P<.001). Furthermore, professional participation in the planning of the portal was positively associated with their support (ß=.57, P<.001). CONCLUSIONS: Findings suggest that assuring good informing, communicating a clear vision to frontline leaders, and acknowledging organizational readiness for change can increase health professional support for electronic health (eHealth) services in the pre-implementation phase. Results highlight the role of frontline leaders in engaging professionals in the planning and implementation of eHealth services and in building health professionals' positive attitudes toward the implementation of eHealth services.