Karnataka cooperation and sugar minister HS Mahadev Prasad died of a heart attack at a private resort in Koppa in Chikkamagaluru district on Tuesday.
Prasad, 58, is survived by his wife and a son.
Local Congress leaders said that they attempted to reach the minister over phone and by knocking the door failed, his room was opened using a spare key and the body was found on a bed.
Officials said that he was in koppa to attend an official function. He had undergone bypass surgery few years ago.
Prasad, represented Gundlupete constituency in Chamarajanagar district, was a close associate of chief minister Siddaramaiah.
Siddaramaiah said "Prasad's death unexpected and shocking. It is a huge personal loss to me and to the Congress party. He was an able administrator and a clean politician. I have lost a close friend and a wonderful colleague."
The state government declared a one day government holiday on Tuesday and announced three days of state mourning.
Prasad was a minister in the JD(S)-BJP coalition government headed by HD Kumaraswamy during 2005-07 and quit JDS and joined the Congress.
Prasad's son Ganesh said the body will be taken to Gundlupete by evening and last rites will be performed on Wednesday.