The Immunization Agenda 2030 (IA2030) has been endorsed at the World Health Assembly as the world's strategy for immunization. The Movement for IA2030 is a voluntary collective of immunization practitioners, principally from low- and middle-income countries, who have pledged to support each other to accelerate local action in support of this global strategy. Collective action is facilitated by the peer learning platform established by The Geneva Learning Foundation (TGLF). We reviewed existing data from Movement participants and collected additional survey data to explore two aspects of sustainability of the Movement: why immunization practitioners participate and how much time and resources they contribute. Quantitative analyses of an existing large data set (n = 5682 participants) were complemented by analyses of data collected through a new survey (n = 291) and focus groups of Movement participants. The most commonly cited reason for participating (32% of responses) was to share experience and learn from others. This was generally true across all levels of experience, gender and place of work, suggesting a common rationale among immunization practitioners in different settings. It was a particularly strong motivation for the most experienced practitioners and those working in a setting with a strong organizational learning culture. New survey data revealed a high degree of intrinsic personal motivation to participate, through commitment of significant time and financial resources, with 47% (n = 136) of respondents committing personal finances to implement an action plan. Focus group discussions provided insights into the implications of findings for sustaining the Movement. Collectively, the analyses highlight key aspects of voluntary collective action to achieve global immunization goals through local action, to inform efforts to ensure long-term sustainability of the Movement.