Togetherness of English for Specific Purposes (ESP) and Task-Based Language Teaching (TBLT) has been the subject of many recent studies in English as a Foreign Language (EFL) and English as a Second Language (ESL) domain. Few studies, however, have addressed the impact of TBLT on ESP learners’ linguistic production. This study aimed at investigating the impact of task-based teaching on ESP learners’ speaking and writing. Furthermore, this study aimed to explore the ESP learners’ and instructors’ attitudes toward the nature of program and their perceived needs of tasks to be accomplished in the course. To fulfill this aim, 60 ESP students majoring in Law in 2 different classes at Allameh Tabataba’i University, Iran, and 10 ESP instructors were selected as the participants of the study. Accordingly, the students in one of the two classes received a one-semester long instruction based on the principles of TBLT as the experimental group, while the students in the other class were taught according to the content of the textbook developed for such courses. After the instruction was over, the students were given a set of standardized and teacher-made tests. The results of the data analysis indicated that the experimental group showed a significant difference in terms of improvement in acquiring productive skills. It was also revealed that there were significant differences between the participants’ attitudes regarding the nature of the course and their perceived needs of tasks. The findings of this research could provide an insight into designing opportune syllabi for ESP courses.