The study reported in this article investigated the use of quest-based learning (QBL) in a gamified English as a foreign language (EFL) course at a Japanese university. A mixed methods research design was utilised to explore the effect purposely designed quests can have on EFL students' foreign language (FL) motivation. The study was conducted over a 14-week period with four intact classes of participants (N = 89). The results of the study showed overwhelmingly positive opinions and perceptions towards QBL and provided evidence that QBL can increase intrinsic FL motivation while supporting FL learning. They suggest that the QBL supported intrinsic motivation because they were enjoyable, meaningful, suitably challenging, supported autonomy through quest choice, and interpersonally meaningful. The positive results were attributed to the quest design that leveraged specific aspects of multiple motivation theories (e.g., Self-determination theory, positive psychology). Three aspects that could hinder intrinsic motivation were also identified: (1) difficulty of the quests; (2) time required to complete the quests; and (3) quest choice allowing the participants to avoid certain quests.