Identifying and developing competencies for English medium instruction (EMI) lecturers is crucial for enhancing the quality of EMI courses. This study, conducted in Japanese higher education, aimed to identify and categorize EMI lecturer competencies that students consider essential according to their varying English proficiency levels. Data were collected across 10 online and face-to-face EMI social science courses over three years and involved Japanese and international students (N = 150). Key findings revealed that students slightly prioritized pedagogic competencies over lecturers’ linguistic abilities, highlighting that clear lesson planning, structured content delivery and fostering student interaction through learner-centred teaching methods are essential, regardless of students’ English proficiency. Meanwhile, linguistic clarity, particularly the use of accessible vocabulary and regular paraphrasing, emerged as crucial for effective instruction. Socio-emotional support, emphasizing empathy and addressing student anxiety, was identified as vital for fostering a conducive learning environment. Based on these findings, we propose a set of core lecturer competencies essential for effective teaching and learning in EMI social science courses.