ECEC-based physical activity (PA) interventions have reported modest changes; however, those that are underpinned by theory seem to report more favorable outcomes. To date, no ECEC-based PA interventions have been underpinned by professional development-focused theories, despite professional development being a consistent component in such interventions. The aim of this study was to describe how the Healthy Online Professional Program for Early Learners (HOPPEL) intervention was underpinned by the concept of a community of practice (CoP) (a theory that focuses on professional development) and to examine the alignment of the designed intervention with the applied theory. The 12-week HOPPEL program comprised a face-to-face workshop and asynchronous/synchronous online sessions. The program was mapped to the CoP elements prior to implementation and then alignment was confirmed following implementation. Quantitative data (i.e., educator demographics, professional development experience) were collected from questionnaires. Qualitative data (i.e., transcripts from the online components) were analyzed using NVivo for themes that aligned with CoP. Post-intervention analysis suggested that the Practice element of a CoP was less well aligned than initially thought. This study aimed to investigate the use of an alternate theory in an ECEC-based PA intervention: using such theories may contribute to greater success in future programs.