Seaweed aquaculture can enhance a range of ecosystem services (ES). Provisioning ES are well quantified and valued, but regulating and maintenance ES are typically more difficult to assess. Here, 134 studies from 30 countries that measure climate regulation, water-quality regulation and habitat provision were reviewed. Quantification estimates were highly context-specific and variable, and very few studies contained valuation estimates. This meta-analysis estimates that seaweed aquaculture can remove a median of 384 kgCha−1yr−1 through net mitigation, 725 kg C ha−1yr−1 through sedimentary burial and/or deep-sea export and 1,546 kgCha−1yr−1 through biomass accumulation. It can remediate 83 kgNha−1yr−1 and 23 kgPha−1yr−1, and provide habitat for between 7-51 taxa. There is reasonable evidence that seaweed aquaculture can enhance water quality, however, climate regulation and habitat provisioning are more difficult to substantiate. Uncertainty about the ultimate fate of carbon, the lack of industrial-scale life-cycle assessments and methodological differences suggest it cannot be stated that seaweed aquaculture universally enhances climate regulation. Further efforts should focus on assessing multiple aspects of ES delivery using standardized Monitoring, Reporting and Verification (MRV) methods over longer timescales, allowing the responsible development of this industry, with climate regulation, water-quality regulation and habitat provision as potential co-benefits to biomass production.