The COVID‐19 pandemic led to significant adaptations to healthcare. Provision of mental healthcare in a changing environment presented healthcare workers with unique challenges and demands, including changes in workload and expectations. To inform current and future healthcare service responses, and adaptations, the current review aimed to collate and examine the impact of the pandemic on mental healthcare workers (MHWs). We conducted a rapid systematic review to examine the overall impact of the COVID‐19 pandemic on MHWs. Searches were conducted in Ovid Medline and PsycInfo and restricted to articles published from 2020. Inclusion criteria specified articles written in English, published in peer‐reviewed journals, and that examined any outcome of the impact of COVID‐19 on MHWs; 55 articles fulfilled these criteria. Outcomes were categorized into ‘work‐related outcomes’ and ‘personal outcomes’. Mental healthcare workers worldwide experienced a range of work‐related and personal adversities during the pandemic. Key work‐related outcomes included increased workload, changed roles, burnout, decreased job satisfaction, telehealth challenges, difficulties with work‐life balance, altered job performance, vicarious trauma and increased workplace violence. Personal outcomes included decreased well‐being, increased psychological distress and psychosocial difficulties. These outcomes differed between inpatient, outpatient and remote settings. The COVID‐19 pandemic significantly altered the delivery of mental healthcare and MHWs experienced both work‐related and personal adversities during the COVID‐19 pandemic. With the continuation of changes introduced to healthcare in the initial stages of the pandemic, it will be important to maintain efforts to monitor negative outcomes and ensure supports for MHWs, going forward.