In addition to urgently needed emission reductions, the IPCC Special Report on Global Warming of 1.5°C highlighted with high confidence that all projected pathways that limit warming to 1.5°C also require the use of Negative Emission Technologies (NETs). The majority of NETs research has focused on land-based methods, however, meeting climate mitigation targets with land-based NETs alone, will be extremely difficult, if not impossible. NET knowledge on the ocean-based counterpart, which has a considerably higher capacity to store carbon, remains limited. OceanNETs will investigate the feasibility and impacts of emerging ocean-based NETs through a transdisciplinary research approach. We will establish if ocean-based NETs can play a substantial and sustainable role in medium-to-long term pathways that achieve climate neutrality from the perspective of reaching the Paris Agreement goals. The impacts of ocean-based NETs on society and the Earth system will also be determined. The respective policy challenges, as well as the implications of interactions between ocean- and terrestrial-based NETs in these pathways, will also be assessed. Analyses will account for both risks and co-benefits, as well as any feedbacks these may have on NET efficacy and feasibility. The project will contribute to major international, national, and EU assessments of possible climate mitigation options. OceanNETs breaks new ground by bringing together recognized NET experts from economic, political, legal, social, and natural sciences and establishing a tight dialogue with stakeholders in a single integrated project. The scientific experts will synergistically work in parallel and together, whilst interacting with stakeholders, to evaluate ocean-based NETs within a UN sustainable development goals framework. The strength of OceanNETs lies in its transdisciplinary approach as opposed to existing disciplinary studies.