Addressing the mental health needs of healthcare staff exposed to psychologically traumatic events at work during the COVID-19 pandemic is a pressing global priority. We need to swiftly develop interventions to target the psychological consequences (e.g., persistent intrusive memories of trauma). Interventions for healthcare staff must be brief, flexible, fitted around the reality and demands of working life under the pandemic, and repeatable during ongoing/further trauma exposure. Intervention delivery during the pandemic should be remote to mitigate risk of infection; e.g., here using a blend of digitalized self-administered materials (e.g., video instructions) and guided (remote) support from a researcher. This parallel groups, two-arm, randomised controlled trial (RCT) with healthcare staff working during the COVID-19 pandemic is the first evaluation of whether a digitalized form of a brief cognitive task intervention, which is remotely-delivered (guided), reduces intrusive memories. Healthcare staff who experience intrusive memories of work-related traumatic event(s) during the COVID-19 pandemic (≥2 in the week before inclusion) will be randomly allocated (1:1) to receive either the cognitive task intervention or an active (attention placebo) control, and followed up at 1-week, 1-month, 3-months, and 6-months post-intervention. The primary outcome will be the number of intrusive memories reported during Week 5; secondary and other outcomes include the number of intrusive memories reported during Week 1, and other intrusive symptoms. Findings will inform further development and dissemination of a brief cognitive task intervention to target intrusive memories.