Chalasani, who served the firm for 18 years, will leave "towards the end of the year to pursue his entrepreneurial ambitions and relocate overseas," Reliance Power said in a stock exchange filing.
Chalasani did not take phone calls seeking comments.
After starting his career with state-run NTPC, Chalasani went with the Anil Ambani Group when the Dhirubhai Ambani empire was split between brothers Mukesh and Anil in June 2005. He handled various assignments for Reliance Power.
A close associate of Anil Ambani, Chalasani, 55, rose to become Chief Executive Officer of Reliance Power in March 2008 and spearheaded its operations.
During his tenure as CEO, Reliance Power won three ultra mega power projects worth Rs 20,000 crore each in Sasan (Madhya Pradesh), Krishnapatnam (Andhra Pradesh) and Tilaiya (Jharkhand).
Reliance Power also signed a USD 10 billion deal with China's Shanghai Electric Corporation to secure equipment supply for its power projects for 10 years in October 2010.
The company said it will name a new CEO in due course.
Reliance Power shares closed at Rs 70.70, down 1.05 per cent on the BSE.