Despite the widely recognized importance of metacognition in language learning, relatively few empirical studies have investigated the role of metacognitive strategies with a cross-linguistic perspective. Drawing on the mixed-method design combining questionnaire and interview data, this study systematically investigated the effects, the transfer potential, and the cross-language facilitation of metacognitive strategies between L1 and L2 contexts. Structural equation modelling (SEM) and multigroup analysis results revealed that metacognitive strategies afforded a more prominent predictive role in English (L2) writing than in Chinese (L1) writing; such strategy use transferred between the two writing contexts, which kept invariant between lower- and higher- L2 proficiency groups and between English and non-English major groups; and there was a cross-language facilitation effect of L1 writing metacognitive strategies on L2 writing performance via the mediation of L2 writing metacognitive strategies. Complementary to the quantitative results, the qualitative interview data was analyzed to provide deep insights into the participating students' metacognitive strategy use in the two task-situated writing. Findings are extensively discussed to offer theoretical and pedagogical implications in this domain.