The Zindagi Mehfooz (safe life; ZM) electronic immunization registry (EIR) is a comprehensive suite of digital health interventions that aims to improve equitable access, timeliness, and coverage of child immunizations through a smartphone-based app for vaccinators, web-based dashboards for supervisors and managers, text message alerts and reminders for caregivers, and a call center. It has been implemented at scale in Sindh Province, Pakistan. This study aimed to present findings from an evaluation of the ZM-EIR suite of digital health interventions in order to improve data availability and use as a contribution, among other immunization program interventions, to enhanced immunization outcomes for children aged 12-23 months in Sindh Province. The mixed methods study included (1) analysis of ZM-EIR system data to identify high-, moderate-, and low-adoption and compliance sites; (2) in-depth interviews with caregivers, vaccinators, supervisors, and managers in the Expanded Program for Immunization (EPI); and (3) pre-post outcome evaluation using vaccine coverage from the Multiple Indicator Cluster Surveys (MICS) 2014 and 2018-2019. Key outcomes of interest were improved data availability, use and contribution to immunization outcomes, including receipt of individual antigens (Bacillus Calmette-Guérin [BCG], pentavalent [Penta] 1-3, measles), full immunization (all antigens), and zero-dose children defined as children aged 6-23 months who have not received the first dosage of the diphtheria-pertussis-tetanus 1/Penta vaccine. By registering newborns, providing alerts and reminders, and tracking their immunization completion, the ZM-EIR improved data availability and use in the EPI. The ZM-EIR was well received by EPI administrators, supervisors, vaccinators, and caregivers. The key benefit highlighted by ZM-EIR users was a list of children who missed scheduled vaccines (defaulters). Through greater availability and use of data, the ZM-EIR implementation, as part of a broader package of immunization program-strengthening activities in Sindh Province, may have contributed to an increase in immunization coverage and timeliness for BCG vaccinations and a decrease in zero-dose children in 2018-2019 from 2014. Additional findings from the study included the dual burden of reporting on paper and gender-related considerations of female caregivers not wanting to provide their phone numbers to male vaccinators, creating barriers to greater uptake of the ZM-EIR. The ZM-EIR is a promising technology platform that has increased the availability and use of immunization data, which may have contributed, along with other intensive immunization program interventions, to improvements in immunization outcomes through systematic registration of children, alerts and reminders, and increased use of data for planning and monitoring by the EPI. ISRCTN Registry ISRCTN23078223; https://doi.org/10.1186/ISRCTN23078223.