Kaya became Director General of RITE in 1998, and then President in 2012. He specializes in systems engineering in the field of energy and environment. The equation called the "Kaya identity" is well-known as an equation for CO2 emissions as the product of carbon intensity, energy intensity and GDP.
After graduating from the University of Tokyo, Kaya was a lecturer, an associate professor, and then professor of the Department of Electrical Engineering at the University of Tokyo.
He is the author of numerous books and papers in the field of energy and environment, published in both Japanese and English.