In the realm of language learning, writing viewed as a discovery process which provides opportunities for ongoing learning. It becomes comprehensible, that the reality of writing itself is a way of structuring, formulating and reacting to the inner and outside worlds. The issue that makes sense at this point is whether and how the study of multiple intelligences and critical thinking could be of any help to students or teachers. This research has attempted to investigate the predictive power of Multiple Intelligences Integrative Tasks (MIIT) and Critical Thinking for successful performance on IELTS Academic Writing. As a result the relationship between the participants' performance on MIIT and IELTS Academic Writing proved by a set of strong and positive Correlation coefficients. In this way a set of strong and positive linear regression demonstrated that the performance on MIIT has predictive power for the IELTS Academic Writing performance. At the end after comparing the effect sizes for both MIIT and Critical Thinking ratings on the IELTS Academic Writing performance, in favor of MIIT, the hypothesis of equal effects rejected successfully.