Objectives: To examine the impact of guided mindfulness practice on psychological distress and psychological capital (hope, optimism, resilience, and efficacy) in doctoral candidates. Participants: Recruitment of a convenience sample of doctoral candidates occurred in July 2015 and participants were randomly allocated to the control or intervention group (38 and 34 participants completed the trial, respectively). Methods: A single-blinded, randomized controlled trial with intention-to-treat analysis was conducted. The intervention consisted of a daily guided mindfulness practice, using an audio CD. Indicators of psychological distress and psychological capital were measured pre- and post-trial with validated questionnaires. Results: Compared to the control group, the intervention group reported a statistically significantly reduction in depression (p = 0.045) and increased self-efficacy (p = 0.004), hope (p = 0.000), and resilience (p = 0.011). Conclusions: These results highlight the effectiveness of self-administered mindfulness practice on the psychological health of doctoral candidates, and the positive effect on psychological capital is reported as a key finding.