This study examines the proximal factors shaping IFRS sustainability self-efficacy among accounting professionals in a Majority World context. Drawing on social cognitive theory (SCT), we conceptualise IFRS sustainability self-efficacy as professionals’ perceived capability to apply sustainability reporting (SR) standards and examine how mastery experiences, vicarious learning and social persuasion, and organisational conditions shape this capability. Using survey data from 1,100 accounting and finance professionals in Nigeria, the findings show that direct involvement in sustainability reporting preparation and review is the strongest determinant of IFRS sustainability self-efficacy. Professional accounting organisation–mandated IFRS sustainability training and access to organisational resources further reinforce self-efficacy, while supportive organisational practices play a complementary role. In contrast, passive exposure, generic sustainability training, and reliance on external consultants exhibit weak or negative effects. Robustness analyses using awareness of SR standards as an alternative outcome confirm a progressive capability pathway from awareness to application. The study contributes theoretically by introducing SCT to IFRS sustainability reporting research and empirically by providing large-scale evidence on the micro-foundations of IFRS sustainability implementation in a Majority World setting. Practically, the findings highlight the importance of experiential learning, professional institutionalisation, and organisational support in translating global sustainability standards into effective reporting practice.