The challenges of higher education can be stressful, anxiety-producing, and sometimes depressing for students. Such negative emotions may influence students' attitudes toward assessment, such as whether it is perceived as acceptable to engage in plagiarism. However, it is not known whether any impact of negative emotions on attitudes toward plagiarism translate into actual plagiarism behaviours. In two studies conducted at two universities (Study 1 N = 718; Study 2 N = 490), we examined whether negative emotionality influenced plagiarism behaviour via attitudes, norms, and intentions as predicted by the theory of planned behaviour. In both studies, negative affect predicted plagiarism intentions mediated by perceived norms, and intentions predicted plagiarism behaviour. These findings suggest that students' negative emotionality is a risk for plagiarism engagement and that higher education institutions should support students' emotional well-being, especially regarding assessment practices.