Ajay Mathur has been the Director-General of the International Solar Alliance (ISA) from March 2021.

Prior to joining ISA, Dr. Mathur was Director General of The Energy and Resources Institute (TERI).

At TERI, he spearheaded the move to accelerate action towards a low-carbon and cleaner economy through the promotion and adoption of renewable energy and green hydrogen in the Indian electricity sector, enhancing efficiency in buildings and industry, and promoting environmental quality through institutional and policy measures to enhance air quality across the country, adoption of resource efficiency and waste recycling measures, and biotechnology-based solutions, especially for agricultural and industrial environment improvement.

He was co-chair of the global Energy Transitions Commission; and of the Clean Cooling Initiatives of the One Planet Summit

He earlier headed the Indian Bureau of Energy Efficiency, and was responsible for its foundational programmes which mainstreamed energy efficiency through initiatives such as the Star Labeling programme for appliances, the Energy Conservation Building Code, and the Perform, Achieve & Trade (PAT) programme for energy-intensive industries.

He was a leading climate change negotiator, and was the Indian spokesperson at the Paris climate negotiations.

He served as the interim Director of the Green Climate Fund during its foundational period.