There is a great deal of individual variability in outcome in second language learning, the sources of which are still poorly understood. We hypothesized that individual differences in auditory processing may account for some variability in second language learning. We tested this hypothesis by examining psychoacoustic thresholds, auditory-motor temporal integration, and auditory neural encoding in adult native Polish speakers living in the UK. We found that precise English vowel perception and accurate English grammatical judgment were linked to lower psychoacoustic thresholds, better auditory-motor integration, and more consistent frequency-following responses to sound. Psychoacoustic thresholds and neural sound encoding explained independent variance in vowel perception, suggesting that they are dissociable indexes of sound processing. These results suggest that individual differences in second language acquisition success stem at least in part from domain-general difficulties with auditory perception, and that auditory training could help facilitate language learning in some individuals with specific auditory impairments.