Past research has found that an individual's academic success, including success in English language learning, can be predicted by a person's 'grit'. Grit is a personality trait defined as the combination of perseverance of effort and consistency of interests. Other than grit, learner engagement is another factor considered to be highly related to levels of academic achievement. However, the paradigm of English language learning has transitioned to online settings. Therefore, it is important to know how students' grit is affected by such a transition. The purpose of this study is to investigate the grit and online engagement of 563 Thai English language learners (ELLs) and to study the relationship between Thai ELLs' grit, learner engagement, and their English language achievement in online settings. Grit scales and online engagement scales were used to collect the data. The present study found that grit positively correlates with language achievement and engagement. Furthermore, it also found that grit is a predictor of language achievement while online engagement demonstrated no predictive value to language achievement. The results are aligned with, and corroborate, the work of Teimouri et al. (2020) suggesting that grit is associated with success in English language learning.