The Purpose Despite a large number of studies in online learning, limited studies have focused on language learners’ metacognition, motivation, and self-efficacy beliefs in the online learning setting. This study attempts to fill this gap by evaluating how the three factors impact learners’ English learning achievement in online learning environments.Design Surveys were administered two times. Data analyses were based on longitudinal mediation analysis. The participants were 590 undergraduate students in China.Findings The results showed a positive and significant correlation among the four variables. Overall, self-efficacy beliefs predicted English learning achievement. The findings support the joint mediating role of metacognition and motivation on the effects of self-efficacy beliefs on English learning achievement.Value The findings support the need to strengthen learners’ metacognition, motivation, and self-efficacy beliefs for online English learning.