Barriers to accessing treatment for Depressive Disorders highlight a need for scalable interventions. Expressive writing (EW), which involves daily writing about a personal issue, has been shown to alleviate depressive symptoms in various samples. Its simple format makes it amenable to online administration. We conducted a multi-methods study to evaluate the feasibility, efficacy, and perceived utility of online EW in patients with Depressive Disorders. We recruited 53 patients diagnosed with a Depressive Disorder from a psychiatry hospital. Half were randomized to complete four 20-minute sessions of EW online and the other half were randomized as controls. All participants completed measures before and after the intervention, and at a one-month follow up. Our primary outcome for feasibility was the number of participants completing at least three sessions of EW, and for efficacy, the primary outcome was depressive symptom severity. Secondary outcomes were anxiety symptom severity, functional impairment, and perceived personal problem complexity. Mixed effect models assessed the impact of condition (EW or control), time, and their interaction on each outcome. Qualitative interviews with 11 participants assigned to EW probed into their experiences, which were subject to reflexive thematic analysis. Most EW participants (73%) completed at least three EW sessions, but only 23% wrote for 20 minutes. There was no evidence that condition interacted with time to impact depressive symptoms (F = 0.10, p = .904), anxiety symptoms (F = 0.17, p = .847), functional impairment (F = 1.03, p = .363), or perceived problem complexity (F = 0.94, p = .394). In qualitative interviews, some participants reported EW allowed them to offload or process negative emotions and thoughts, whereas others reported it to be unhelpful. EW was feasible to administer online to patients with Depressive Disorders, with some reported benefits for emotional and cognitive processing. However, EW was not associated with improvements in symptoms and may not be an effective online intervention for Depressive Disorders in its current state. Providing more guidance, with some clinical oversight or support, may be a promising approach to modifying the intervention in future work. Trial registration: ClinicalTrials.gov NCT06699719