The addition of verbal narration could impede reading performance, called the verbal redundancy effect. Two experiments in this study explored the moderating role of readers’ vocabulary size and text difficulty in this effect. A total of 77 native English speakers in Experiment 1 and 45 non-native English speakers in Experiment 2 were divided into two groups of vocabulary-size in each experiment. In both experiments, participants read eight passages and answered questions. The study manipulated the narration presentation and text difficulty. Experiment 1 showed that adding narration impedes comprehension when high-vocabulary participants read easy passages, whereas it enhances comprehension when low-vocabulary participants read easy passages. The redundant narration effect was moderated by reading skills. Experiment 2 showed no significant narration effect, but comprehension scores were higher when high-vocabulary multilinguals read neutral passages with narration than without narration. These effects are aligned with previous research and well explained by cognitive load theory.