Although an emerging field, seamless learning (SL) can be a powerful tool, and in this study, it was integrated into a peer-assisted learning (PAL) center in such a way to concentrate on the development of undergraduate English writing skills in Thailand. This quasi-experimental quantitative and qualitative study was conducted at an international college, where the control and experimental groups consisted of 18 and 17 research participants, respectively. The objective of this study was to examine whether student involvement in a seamless learning-focused PAL center could help develop academic writing skills of undergraduate students in an international faculty at a private university in Thailand. In this study, the instrument utilized to elicit and collect information was in the form of a sample IELTS writing test, which mirrored Task 2 of the examination. Those providing peer feedback to the participants were their fellow classmates who had achieved a CEFR English level of B2 or higher. There was a total of 48 student peer-mentors (SPMs) in this study. Based on the findings of this study, it can be concluded that by integrating SL into a PAL center, it could significantly develop undergraduate student writing skills. With more and more university faculty budgets becoming smaller, higher educational institutions are being influenced to become more creative in adopting more fiscally responsible academic projects, and seamless learning-focused PAL centers could be implemented in such a way to develop undergraduate student writing skills at little or no cost to universities. The research implications for this study offer a framework on how to better develop academic writing skills for undergraduate students.