A considerable number of those who suffer from depression develop a chronic course of the disorder in which symptoms remain over prolonged periods of time and risk for suicidality is significantly increased. Once patients have entered such a course, response to established treatments is significantly reduced. The aim of the current study was to test the use of Mindfulness-Based Cognitive Therapy (MBCT), a treatment originally developed for prevention of relapse in patients who are currently well, in a chronically depressed group and to investigate its effects on both cognitive and neurophysiological factors known to be involved in the maintenance of the disorder. Participants were randomly allocated to receive either MBCT or treatment-as-usual (TAU) and effects on current symptoms and maintaining factors assessed directly before and after treatment. Results indicated that the treatment is both feasible and acceptable, and that it can bring about significant reductions in depressive symptoms as well as cognitive and neurophysiological vulnerability. The findings suggest that MBCT and the intensive training in mindfulness meditation it encompasses hold considerable promise for addressing the processes involved in the maintenance of chronic and suicidal depression.