Rao suffered a heart attack at his residence at Eluru in West Godavari district as he was leaving to campaign for his daughter, who is contesting the local body election, family members said.
He is survived by wife and two children. The last rites will be performed Sunday.
A key politician from coastal Andhra region, Vidyadhar Rao had served as state minister in the cabinets of N.T. Rama Rao and N. Chandrababu Naidu. He held various portfolios, including agriculture and major industries.
During his political career spanning over three decades, Rao was elected to the assembly five times from Chintalapudi constituency in West Godavari district. He began his political career in 1979.
He was elected to the assembly as an independent in 1983 and a year later joined Telugu Desam Party (TDP) at the invitation of party founder and popular actor N.T. Rama Rao. Vidyadhar Rao was a key minister in Naidu's cabinet. However, in 2004, he lost the elections.
Before the 2009 elections general elections, Vidyadhar Rao quit the TDP to join Praja Rajyam Party (PRP), floated by actor-turned-politician K. Chiranjeevi. Vidyadhar Rao, however, again lost the election.
After PRP's merger with the Congress in 2011, he was appointed Congress spokesperson.
Chiranjeevi has expressed shock over Rao's sudden death. The union tourism minister is rushing to Eluru from New Delhi to attend the funeral.
Chief Minister N Kiran Kumar Reddy, state Congress chief Botsa Satyanarayana, Naidu and other leaders his condoled death.