He was 87 and is survived by his wife, two sons and a daughter. Patnaik was undergoing treatment at a private hospital at Jeypore.
"He died around 8.10 am. He had been unwell for the past few days and was undergoing regular check-ups," family sources said.
Patnaik had joined Congress in 1954 and won the Assembly election from Jeypore in 1961, 1974, 1977, 1980, 1990 and for the last time in 1995. Denied a Congress ticket for Jeypore seat, he contested the Assembly election in 2000 as an Independent candidate and lost the election to the BJD's Rabi Narayan Nanda.
With a political career spanning nearly five decades, Patnak had held portfolios of law, finance and panchayati raj in the state government.
