A significant number of obsessive–compulsive disorder (OCD) patients continue to experience symptoms that interfere with their functioning following cognitive behavioural therapy (CBT). Providing an additional augmentation treatment following CBT could help reduce these residual symptoms. Mindfulness interventions that facilitate less reactivity to thoughts and feelings may be helpful for patients suffering from residual OCD symptoms. The purpose of the current randomized waitlist control trial was to evaluate the feasibility and impact of providing an 8‐week mindfulness‐based cognitive therapy (MBCT) intervention following completion of a CBT intervention to OCD patients who continued to suffer from significant symptoms. Results indicated that compared to the waitlist control group, MBCT participants reported decreases in OCD symptoms (d = 1.38), depression symptoms (d = 1.25), anxiety symptoms (d = 1.02), and obsessive beliefs (d = 1.20) along with increases in self‐compassion (d = 0.77) and mindfulness skills (d = 0.77). Additionally, participants reported high levels of satisfaction with the MBCT intervention. The results suggest that the use of MBCT for OCD as an augmentation therapy is acceptable to patients who continue to suffer from OCD symptoms after completing CBT and provides some additional relief from residual symptoms. Key Practitioner Message Mindfulness interventions teach skills that facilitate disengaging from cognitive routines and accepting internal experience, and these skills may be valuable in treating obsessive–compulsive disorder (OCD), as individuals describe getting “stuck” in repetitive thoughts and consequent rituals. The results of this study suggest that teaching mindfulness skills using an 8‐week mindfulness‐based cognitive therapy (MBCT) intervention provides an added benefit (decreases in OCD, depression, and anxiety symptoms) for patients with OCD who have completed a cognitive behavioural therapy intervention and continued to suffer from significant symptoms. Participation in MBCT was also associated with increases in mindfulness skills including increased ability to be nonjudgmental and nonreactive. By fostering a nonjudgmental stance towards intrusive thoughts, mindfulness may discourage suppression and avoidance of thoughts and this could lead to increased habituation and a decreased reliance on compulsions. The use of MBCT as an augmentation treatment should be further explored to elucidate whether this treatment is beneficial for preventing relapse of OCD and could be compared against further cognitive behavioural therapy to see if offering participants a different and theoretically compelling intervention, such as MBCT, would outperform “more of the same” for individuals with OCD.