In instructional contexts, instructor credibility or ethos is deemed to play a paramount role in teacher–student interaction and relationships. Much effort has been devoted to instructor credibility conceptualization, measurement, and its association with other instructional variables of interest in dominantly quantitative inquiries. However, little research has been undertaken in second-language education in which communication is both a means and an end. This qualitative research set out to explore the perception of the students of instructor credibility in the context of higher English education and how gender, nativeness, and subject matter might impact their perceptions. It also aimed to study how instructor credibility could, in turn, influence the engagement and success of the students. Thirteen senior students of English as a foreign language from a university in Iran participated in this study. They were given a scenario about their prospective professors for two courses of “Research Methodology” and “Essay Writing.” The professors included four native English- and Persian-speaking male and female PhD holders. The participants were, then, interviewed about their perceptions of instructor credibility, their choices of instructors, and how they would affect their engagement. The data were recorded, transcribed, and recursively analyzed using an inductive thematic analysis. While instructor credibility is commonly characterized as a three-dimensional construct, involving competence, character, and caring, the data analysis generated a new component of performance concerned with the effectiveness of classroom knowledge presentation and activity organization. Caring also emerged as a constituent of a more inclusive component of rapport. Interestingly, albeit they viewed native English professors as generally more competent due to their nativeness, they perceived non-native professors as more credible for both courses, mainly because of their rapport building and familiarity with the needs and challenges of the students. Most of the participants also viewed male professors as more competent and communicative for both courses. The participants also tended to argue that perceived instructor credibility would encourage them to put in more effort in their academic undertakings and to engage in class activities. This would ultimately enhance their academic achievements and success. The paper discusses the findings and implications for second-language instructor credibility conceptualization and practice.