Limiting the increase in global average temperature to below 2°C compared to pre-industrial levels will require ambitious mitigation action by a broad range of actors including Parties to the United Nations Framework Convention on Climate Change (UNFCCC), i.e., national governments, and non-party stakeholders (NPS). This paper focuses on three types of NPS, namely, sub-national governments, the private sector and financial institutions, and examines how the 2015 agreement could help the NPS encourage increased mitigation actions as well as the financing for such actions. The paper identifies five barriers that can prevent NPS from enhancing their actions and assesses how the current process under the UNFCCC is addressing these barriers for the pre-2020 period. It also explores options to establish or enhance links between the UNFCCC and NPS in the 2015 agreement for post-2020, in order to further address the barriers and enhance actions by NPS.