Approximately one in three post-secondary students experience clinical levels of anxiety or depression during their academic career, with many students not receiving treatment. Internet-delivered cognitive behaviour therapy (ICBT) is an alternative to face-to-face services that is effective in general adult populations, but has been associated with high attrition rates and smaller effect sizes in student populations. In this implementation trial, the efficacy and uptake of an ICBT course for anxiety and depression (i.e. the UniWellbeing Course) was examined in Saskatchewan. Given the evidence from the face-to-face literature, the role of motivational interviewing (MI) and booster lessons was also examined. Using a two-factor design (factor 1: online MI); factor 2: booster lesson), a total of 308 clients were randomized to one of four groups: standard care (n = 78), MI (n = 76), booster (n = 77), and MI + booster (n = 77). Overall, 89.9% (n = 277) of clients started treatment. The aims of the study were to assess (1) the efficacy of the UniWellbeing Course in reducing symptoms of anxiety and depression and increasing perceived academic functioning; (2) the impact of a pre-treatment MI component on attrition and engagement; (3) the impact of a booster lesson on depression, anxiety, and perceived academic functioning at 3-month follow-up; and (4) the combined effect of MI and booster. Overall, students reported significant, large decreases in symptoms of depression (Cohen’s d: 1.25 – 1.67) and anxiety (Cohen’s d: 1.42 – 2.01) from pretreatment to post-treatment, with 47.5% and 56.6% of clients experiencing reliable recovery on measures of depression and anxiety, respectively. Small, but significant, effects were seen for improvements in perceived academic functioning across the four conditions (Cohen’s d: 0.20 – 0.48). Changes were maintained at 1-month and 3-month ii follow-up on all primary measures across conditions. Overall, 54.0% (n = 150) of clients accessed all four lessons of the UniWellbeing Course. The addition of pre-treatment MI did not confer improvements to treatment completion rates or engagement (e.g., mean logins or messages sent to therapists). Small between-group effects were seen in favour of MI for depression (Cohen’s d: 0.23), anxiety (Cohen’s d: 0.25), and mental healthrelated disability (between-group Cohen’s d: 0.35) at post-treatment. In terms of the booster lesson, only 30.9% (n = 43) of clients accessed the booster lesson, although clients who accessed it were satisfied with the content and timing of the booster overall. Between-group effects were not significant for the booster at 3-month follow-up. Subanalyses comparing clients who utilized the booster to those who did not were underpowered, but revealed a larger decrease in depressive symptoms (between-group Cohen’s d: 0.31) at 3-month follow-up. No advantage was found for the combination of MI and booster on treatment completion, engagement, or outcomes. Overall, there is some evidence to suggest that including MI at pre-treatment results in greater symptom reduction although these benefits do not persist to 1-month and 3-month follow-up. The inclusion of a self-guided booster lesson may also help with continued symptom management up to 3-month follow-up, but low uptake is a barrier to clients experiencing these benefits. Uptake of the course was highest among White female participants and at large universities, suggesting a need for alternative recruitment strategies to increase uptake among other student populations. Findings from this trial contribute to the literature on improving ICBT outcomes for post-secondary students.