The study investigated the role of word-level and verbal skills in writing quality of learners who spoke English as a first (L1) and second (L2) language. One hundred and sixty-eight L1 and L2 learners (M = 115.38 months, SD = 3.57 months) participated in the study. All testing was conducted in English. There was a statistically significant L1 advantage on the measures of writing quality and verbal skills (i.e., vocabulary, verbal working memory, and semantic fluency) but not on word-level skills (i.e., spelling and word reading). Results from the multi-sample structural equation modeling analysis showed that the word-level and verbal skills made independent contributions to writing quality of L1 and L2 learners and the strength of these relationships was invariant (equivalent) across the two samples. The educational implications of research on L2 learners who are learning to write in a majority language were discussed.