Due to the potent role of critical thinking in learners’ academic success and its connection with factors conducive to learning such as argumentation ability, the present study seeks to primarily probe the correlation between Iranian EFL learners’ critical thinking ability and their argumentative writing achievement, and investigate the predictability of the students’ argumentative writing achievement based on their scores on critical thinking scale. Furthermore, the effect of gender on Iranian EFL learners’ argumentative writing achievement was investigated. In so doing, 'Watson-Glaser Critical Thinking Appraisal' (2002) as well as an argumentative writing assignment was employed, and the participants of the study included 178 EFL learners in three universities in Mashhad, Iran. Structure Equation Modeling (SEM) was utilized to analyze the data. The results substantiated the positive correlation between critical thinking ability and argumentative writing revealing that these two variables significantly and positively related to each other among the predictors (subscales of the critical thinking) of argumentative writing, inference, assumptions, arguments were the stronger predictors. Finally, gender was not found to significantly affect Iranian EFL learners’ argumentative writing achievement. The conclusions and implications of this study are pointed out with reference to foreign language teaching context.