While formal, digital-technology-based professional development for higher education faculty has been extensively studied, informal and incidental learning (IIL) within this area remain underexplored. Integrating the Broaden-and-Build Theory with the Informal and Incidental Learning framework, this study examines how positive emotions influence faculty's social media engagement and trigger work-related IIL, which subsequently enhances professional learning. Interviews were conducted with nine expatriate faculty at a Sino-British transnational university. The narrative analysis reveals how social media engagement, facilitated by positive emotions, connects personal interests with professional needs to generate self-directed professional development. This study highlights the value of social-media-based learning by distinguishing nuances between informal learning and incidental learning. Findings suggest that social-media-based IIL addresses individualised, real-world challenges like cross-cultural competencies. Implications for higher education policymakers emphasise the need for building a holistic professional learning environment where faculty's self-initiated IIL is possible through digital platforms to meet their diverse, tailored needs for professional growth.