To ease the shortage of professionals, lay volunteers were trained to become health promoters and role models for a large community program to enhance physical activity, well-being, and neighborhood cohesion in socioeconomically disadvantaged groups in Hong Kong. This study aimed to examine the effects on health promoters (trainees) and the feasibility and acceptability of capability-building train-the-trainer workshops (TTTs) using Zero-time Exercise (ZTEx) to implement a community program for about 1,000 participants. A four-session (totally 8 hours) TTT introduced an evidence-based ZTEx intervention to enhance physical activity and well-being, and build capacity for community program implementation. Twenty-eight trainees actively participated in the TTT. Twenty-five and 21 trainees completed the 1- and 3-month questionnaires, respectively. Eleven trainees attended the 1-year focus group interview. Repeated measures analysis of variance and Friedman test were used to compare the parametric and nonparametric data, respectively. Qualitative data were analyzed using thematic content analysis. The trainees reduced their sedentary behavior and improved their interpersonal communication skills, knowledge, and attitude toward ZTEx, grip strength, balance, and perceived well-being. The community participants reported improvements in neighborhood cohesion and grip strength. The 1-year qualitative results supported the 3-month quantitative findings. This brief and innovative TTT affirmed the feasibility of using ZTEx and the role modeling approach for lay health promoters to reduce sedentary behavior and enhance physical activity, fitness, and well-being. They then contributed to the successful implementation of community programs that benefited many. This study provides a new model for building capacity for health promotion in the community.