Karunadasa grew up in Colombo. She attended high school in Sri Lanka and was a student at Ladies College, Colombo. She thought that she would become a doctor, and eventually decided to apply to university in America. She attended Princeton University, where she worked with Robert Cava on the geometric magnetic frustration of metal oxides. Cavas excitement about research inspired Karunadasa to continue her own academic career. Graduating with a degree in chemistry and a certificate in materials science and engineering, Karunadasa joined the University of California, Berkeley for her doctoral studies. There she worked in the lab of Jeffrey R. Long on heavy-atom building units for magnetic materials and electrocatalysts for water splitting. Karunadasa continued her work on water-splitting electrocatalysts with Jeffrey R. Long and Christopher Chang as a postdoctoral fellow. The molybdenum-oxo metal complex synthesized by Karunadasa is around seventy times cheaper than platinum, the most commonly used metal catalyst in water splitting. She then moved to the California Institute of Technology, where she worked on catalysts for hydrocarbon oxidation with Harry B. Gray as a BP Postdoctoral Fellow.