Grieving is a natural process, and many people adjust with support from family and friends. Around 40% of people would benefit from additional input. Online bereavement support interventions may increase access to support. Evidence regarding their acceptability and effectiveness is emerging but needs to be synthesised. To synthesise evidence on the feasibility, acceptability, effectiveness, impacts and implementation of online interventions to improve wellbeing, coping and quality of life after bereavement. A rapid review of evidence regarding online bereavement support. We appraised study quality using AMSTAR 2 and the Mixed Methods Appraisal Tool. English language articles published 1 January 2010 to 4 January 2024, using Ovid MEDLINE, Ovid Embase and APA PsycINFO. Eligible articles examined formal and informal online interventions to improve bereavement outcomes. We screened 2050 articles by title and abstract. Four systematic reviews and 35 individual studies were included. Online bereavement support was feasible, acceptable and effective in reducing grief intensity, stress-related outcomes and depression. Where reported, participant retention was typically >70%. Positive impacts included: access to a supportive community at any time, reduced isolation; opportunities to process feelings; normalisation of loss responses; access to coping advice and opportunities for meaning-making and remembrance. Negative impacts included upset due to insensitive comments from others via unmoderated online forums. Online interventions can widen access to acceptable, effective bereavement support and improve outcomes for bereaved people. National policies and clinical guidelines relating to bereavement support need to be updated to take account of online formats.