Building teachers' professional capital as a mix of human, social and decisional capital is a prominent strategy to transform the teaching profession and ensure quality education. However, a scant of evidence is available about the determinants of professional capital development in Ethiopia. This study examined the link between engagement in diverse professional learning activities, job satisfaction, and teacher professional capital development using data from 302 primary school teachers of Banja Woreda, Amhara Region, Ethiopia. SEM analysis suggested that teacher engagement in individual professional learning activities and job satisfaction directly influences professional capital development, and teacher engagement in collaborative professional learning activities indirectly influences professional capital development through job satisfaction. Mediation analysis revealed that teacher job satisfaction partially mediates the effect of engagement in individual professional learning activities and fully mediates the effect of engagement in collaborative professional learning activities on teachers' professional capital development.