This study investigates how task complexity shapes motivation and performance in second language (L2) pragmatics, a domain that remains underexplored within task-based learning research. To address this gap, 37 secondary school learners of English completed both simple and complex decision-making tasks at three intervals over an eight-week period. Task complexity was manipulated through adjustments to intrinsic task elements and reasoning demands. Motivation was assessed via Likert-scale questionnaires, semi-structured interviews, and an analytical turn-taking metric, while performance was measured through pragmatic complexity and accuracy in suggestion speech acts. The findings revealed that higher self-reported motivation corresponded with increased pragmatic complexity and accuracy, particularly during more cognitively demanding tasks. Additionally, motivation was found to fluctuate according to cognitive load, underscoring the significance of task relevance and contextual factors in sustaining learner engagement over time. These insights contribute to a deeper understanding of the dynamic interplay between motivation and cognitive complexity in L2 pragmatics and offer valuable implications for pedagogical practice and future research.