The poor student performance in the Programme for International Student Assessment has urged the Malaysian authorities to upskill teachers' professional learning. However, little is known about how instructional leadership contributes to teacher professional learning, especially in the Malaysian context. This study seeks to investigate the direct relationship between principal instructional leadership and teacher professional learning through the mediating effects of teachers' trust in the principal and self-efficacy in a multiple mediated-effects model. Data were collected from 335 primary and secondary school teachers in Penang, Malaysia. A partial least squares structural equation modelling approach was used for data analysis. The results found that the relationship between principal instructional leadership and teacher professional learning is mediated by teachers' trust in the principal and self-efficacy. Implications for theory and knowledge are presented.