Yadav, who was 93, is survived by four sons.
His last rites will be performed tomorrow in his native Meharban Singh Ka Purwa village here, his son and SP leader Chaudhary Sukhram Yadav said.
"He passed away around 4 this morning suddenly. He was a heart patient but was doing fine of late. He chaired a programme as recent as last week in which chief minister Akhilesh Yadav was present", Sukhram said.
Assembly Speaker Mata Prasad Pandey and senior minister Shivpal Yadav have already arrived to pay their last respects and Akhilesh Yadav and SP supremo Mulayam Singh Yadav are expected soon.
The leader was a two-time MP of the Rajya Sabha and three-time MLC, Sukhram said.