The political success of the Paris COP 21 in 2015 contrasted sharply with the diplomatic breakdown at Copenhagen six years before in 2009. Contributing to this success was China’s emergence as a more positive participant in the international climate change negotiations. Despite efforts to reduce energy and carbon intensity since the mid-2000s, Chinese negotiators in Copenhagen were careful not to link domestic action on climate change to any presumptions of international obligation. This stands in marked contrast to Paris where, for the first time, China was willing to commit to an absolute cap on emissions subject to international measurement, reporting, and verification (MRV). This article examines what changed between 2009 and 2015 such that China was able to play a more constructive role in the global climate regime. It argues that a key driver of change was China’s shift to a ‘New Normal’ model of economic development. Beginning in the 12th Five Year Plan Period (2011–2015), China’s economic policy prioritized a transition from energy-intensive growth based on heavy industry, exports and investment, to a more balanced economy characterized by slower growth, an increasing role for services and domestic consumption, and a focus on innovation and low-carbon technologies. This transition gave China the opportunity to re-formulate its priorities in international climate negotiations and helped pave the way for increased climate cooperation with the US, the lack of which had been a major roadblock to success in Copenhagen. Progress was further facilitated by a range of external factors, including impressive French diplomacy in the run-up to COP21 and the important shift to a bottom-up, voluntary approach to commitments.Policy relevanceThis article analyses the reasons behind China’s more constructive engagement at COP 21 in Paris, which contributed to the Conference’s successful outcome. It is important for policy makers to better comprehend China’s shifting position and the motivations behind it, given the country’s key role in keeping temperature rise at a safe level. The deal reached in Paris now needs to be implemented, and success is by no means guaranteed. A deeper understanding of the position of this key player can only help with the negotiation process, implementation phase, and further negotiations that are needed to strengthen targets.