Critical thinking is a multifaceted construct involving a set of skills and affective dispositions together with self-regulation. The aim of this study was to explore how self-regulation and effort in test-taking contribute to undergraduate students' performance in critical thinking assessment. The data were collected in 18 higher education institutions in Finland. A total of 2402 undergraduate students at the initial and final stages of their bachelor degree programmes participated in the study. An open-ended performance task, namely the Collegiate Learning Assessment (CLA[plus]) International, was assigned to assess students' critical thinking, and a self-report questionnaire was used to measure self-regulation and effort in test-taking. Information on test-taking time was also utilised in the analysis. The interrelations between the variables were analysed with correlations and structural equation models. The results indicate that self-regulation in test-taking has only indirect effects on critical thinking performance task scores, with effort and time as mediating variables. More precisely, planning contributed to critical thinking performance indirectly through test-taking time and effort, while monitoring had no significant relation to critical thinking performance. The findings did not differ between the initial-stage and final-stage students. The model explained a total of 36% of the variation in the critical thinking performance task scores for the initial-stage students and 27% for the final-stage students. The findings indicate that performance-based assessments should be carefully designed and implemented to better capture the multifaceted nature of critical thinking.