An electronic immunization information system (IIS) should support the administration of vaccinations in primary care, enable follow-up for immunization schedules, and facilitate efforts to increase vaccine coverage. This study aimed to evaluate the benefits associated with the implementation of a province-wide IIS in Quebec, Canada, using the Benefits Evaluation Framework. A mixed-methods approach method was employed, including individual interviews, a survey, and a time-and-motion study. Interviews were conducted with 20 key informants identified in collaboration with the Quebec Ministry of Health and Social Services (French acronym: MSSS). Following the implementation of IIS, the MSSS distributed an email invitation to all potential system users across Quebec to participate in the survey. In addition, a time-and-motion study was conducted with IIS users at eight community health centers. Most survey participants (n = 651) reported positive perceptions regarding service quality, system usability, and the completeness of information provided by the IIS. The system was found to improve user productivity, and users reported a high level of satisfaction. Satisfaction was associated with information, service, and system quality, while productivity was further associated with both satisfaction and frequency of weekly system use. However, the results did not support a significant association between user satisfaction and overall system use. The time-and-motion study revealed no significant differences between sites in the mean duration required to perform various system tasks. Interviews also highlighted the existence of barriers to successful IIS implementation, such as resistance to change and insufficient resources. Despite limited supporting resources, the implementation of the provincial IIS in Quebec was generally successful. User acceptance emerged as a critical factor for the widespread adoption of future health information systems.