Reddy was elected as the president of his college student's union while studying medical science in M R Medical College of Gulbarga University, in neighboring Karnataka.
In 1975, he was made the President of the Cuddapah District Youth Congress Committee. In 1978, he made his debut to Andhra Pradesh Assembly from Pulivendula and retained the seat for six terms.
Reddy was one of those rare politicians of the country who never tasted defeat in electoral politics.
In 1980, YSR became Minister of State for Rural Development, in the Tengutri Anjaih Government.
In 1982, he became the Cabinet Minister for Excise and also held the charge of Education and Health department in 1983.
YSR had earned the title of 'Cuddapah Tiger' for his aggressive role in the state assembly.
YSR became the state party president at the age of just 34.
In 1985, Reddy quit his position of APCC president.
In 1989, he re-entered the political arena and was elected to the Lok Sabha from Cuddapah. He represented the constituency in four Lok Sabha.
In 2003, YSR undertook a three month long paadayaatra, of nearly 2000 kilometer across the state. That helped him to become Chief Minister.
The Indian National Congress won both in the general and assembly elections of 2004 ensuing that Reddy became the 23rd Chief Minister of Andhra Pradesh.
Reddy came back to power in 2009, with a slogan 'Development and the credibility.'
In the elections, Congress secured the required majority in the assembly with 156 seats and also won 33 Lok Sabha seats.
Reddy is survived by wife Vijaya Lakshmi, son Y S Jagan Mohan Reddy and daughter Sharmila. Jagan Mohan.