This study investigates the effectiveness of the Comprehensible Input (CI) approach in enhancing English-speaking skills among non-English major university students in Vietnam. Based on Krashen’s Language Acquisition Theory (1985), a quasi-experimental design involved 360 students randomly assigned to an experimental group (CI-based instruction) and a control group (traditional grammar-based instruction). Pre- and post-tests assessed fluency, pronunciation, vocabulary, and communicative competence. Qualitative data from surveys and interviews complemented the findings. The CI group showed significant improvements across all domains (p < 0.001), with increased confidence and engagement. Qualitative results supported CI’s effectiveness in fostering natural language use. This study advocates CI as a valuable strategy for EFL contexts and suggests practical applications for curriculum development in Vietnamese higher education.