The present study aimed to empirically examine the validity of grit among language learners and its relation to vocabulary knowledge. Grit is defined as a trait that is characterised by a tendency to be passionate about and persevere towards the achievement of long-term goals. A newly developed questionnaire, L2-Grit Scale, which assesses perseverance of effort and consistency of interest in language learning was used. The construct validity was evaluated, and bi-factor CFA was supported. The convergent and divergent validity of the grit constructs were tested against operationalisations of related motivational constructs. The results suggest that the L2-Grit Scale is, reliable, valid and suitable for use in L2 research. With regard to predictive validity, grit has shown to have a non-significant direct effect on later vocabulary knowledge. Rather, initial grit was only indirectly associated with later vocabulary knowledge through the mediation role of later endorsement of grit.