Metacognition is has been shown to play an important role in students' academic success and in their language learning process in particular. Therefore, it should be fostered among language learners. The present study sought to explore metacognition including metacognitive knowledge and metacognitive skills among non-English-major university students in the Vietnamese context. Questionnaires and semi-structured interviews were employed to collect data in a convergent parallel design of mixed methods research. A total of 1,565 undergraduates from seven public universities completed the surveys, 13 of which participated in the interviews. The findings indicated a high level of consistency between two types of data and showed that the students had sound metacognitive knowledge of the self and the learning context. However, they lacked metacognitive knowledge of the language matters and the learning process and were not proficient in metacognitive skills (i.e., planning, monitoring, and evaluating). Moreover, there were significant differences in metacognitive knowledge and metacognitive skills in terms of gender and years of study. Metacognitive skills were significantly different in terms of marks in the previous English course. but not in terms of metacognitive knowledge among students. Accordingly, the study put forward several important implications at macro-, meso-, and micro-levels to contribute to the improvement of metacognition among English as a foreign language learners in the Vietnamese context as well as the other international English as a foreign language context.