This study investigated the effects of strategic planning and task structure (personal, narrative, and decision-making tasks) on L2 writing outcomes. One hundred and twenty intermediate English as a foreign language learners were randomly divided into strategic-planning and no-planning-time groups. The strategic-planning group performed the three tasks in a simple-complex sequence, whereas the no planning group completed the tasks in a random sequence. Their essays were analyzed using complexity, accuracy, fluency, and lexis measures. The results revealed that strategic planning with simple-complex sequencing resulted in positive effects on the four constructs of L2 written production, as compared with no planning with random sequencing. Additionally, task structure positively influenced syntactic complexity, lexical complexity, and one subconstruct of accuracy, but not fluency. The structured and less structured tasks (i.e., personal and narrative) through the provision of planning time produced greater accuracy and lexical complexity, whereas the unstructured task (i.e., decision-making) through the provision of planning time favored syntactic complexity. Finally, the results showed that the interaction between strategic planning and task structure led to substantial effects on syntactic complexity and one subconstruct of accuracy. These findings give additional support to the limited attentional capacity hypothesis and the tradeoff hypothesis. Methodological and pedagogical implications of the findings for task design and implementation condition in L2 writing are discussed.