Opioid-related harms have been increasing in Australia over the last 5 years. Patients with opioid use disorder are over-represented in ED presentations. Opioid agonist treatment is the most effective community-based treatment. Buprenorphine is considered the safest of these treatments to use in the ED setting. This rapid review investigated the effectiveness of initiating buprenorphine in the ED setting. Medline, Embase, Emcare, PSYCinfo, CINAHL and Cochrane Central Register of Controlled Trials databases were searched. Randomised and non-randomised studies published in peer-reviewed journals that involved the initiation of buprenorphine in the ED setting were considered eligible. The search revealed 350 articles of which 11 were included in the review; three articles representing two randomised controlled trials (RCTs) and eight observational studies. Data were extracted from included papers and risk of bias assessed on the RCTs. One well-conducted RCT showed that buprenorphine initiated in the ED does improve treatment engagement up to 2 months after an ED visit. Eight observational studies, one with a comparator group reported positive results for this intervention. There is strong evidence that clinicians should consider commencing buprenorphine in the ED for patients with opioid use disorder when combined with a direct and supported referral or 'warm handover' to community care. Further implementation studies and investigation of long-acting injectable buprenorphine treatment are required.