Globally, the COVID-19 pandemic has compelled educational institutions to explore alternatives to face-to-face instruction. The primary objective of this study is to identify the teacher’s role in the English argumentative writing performance of low proficiency university students via WhatsApp. In this case study, data were collected from multiple resources including WhatsApp discussions, interviews and students’ argumentative writing on thirteen undergraduate students from Universiti Sains Malaysia, chosen based on their Malaysian University English Test (MUET) results. The argumentative writing essays that the students sent every week for eight weeks after three days of discussion in WhatsApp with the teachers based on eight topics. The students' writing scores revealed that teacher’s role helped students’ improved in their writing skills and the students’ attitudes. The findings suggest that WhatsApp is recommended to support the students in writing, highlight the importance of teacher’s role in the students’ motivation, engagement and effective learning.