This article presents results of a systematic review and meta-analysis to further investigate the impact of unilateral cochlear implantation (CI) in adults with single-sided deafness (SSD) with regards to speech perception in quiet and noise, tinnitus, sound localisation and quality of life (QoL). Many more publications since the last systematic review in 2015 have enabled a meta-analysis to be performed. A database search across Medline, Embase and PubMed was conducted on 31 December 2020 according to PRISMA guidelines. Initial search included reports with patients having unilateral severe to profound deafness with normal or near-normal hearing in the other ear. Articles were evaluated by two independent reviewers. Risk of bias assessment was performed using the Joanna Briggs Critical Appraisal Checklist for Case Series. All scaled outcomes measuring speech perception, tinnitus, sound localisation and QoL, which included at least two independent studies, were meta-analysed. Of 2309 studies identified, 50 were included comprising 674 patients aged 19 to 93 years with duration of deafness of 0.8 to 68 years. Speech perception: 34/38 studies showed statistically significant improvement in speech perception, with meta-analysis of five studies showing improvement of speech understanding following CI. Tinnitus: 21/21 studies reported statistically significant mean reduction in tinnitus, with meta-analysis of seven studies showing statistically significant reduction in tinnitus. Sound localisation: 24/27 studies reported statistically significant improvement in sound localisation with seven meta-analysed studies collectively showing improvement. QoL outcomes: 21/22 reported significant improvement, with eight meta-analysed studies collectively showing improvement. Limitations include heterogeneity in test methods and definitions of SSD used, variable follow-up times (six months to 3.5 years), small sample sizes in some studies (three to 70), and inability to control for aetiology, onset and duration, age at CI, device manufacturer and rehabilitation. Despite this, the present review shows that CI in adult patients with SSD gives rise to improvement in speech perception, tinnitus control, sound localisation, and QoL.