BJP MLA Devendra Pratap Singh died on Monday morning following a cardiac arrest.
He was 55.
The MLA from Amapur was rushed to a district hospital, where doctors declared him dead, family sources said.
"Singh was brought to the hospital around 7 am and he was pronounced dead," Chief Medical Superintendent of the hospital Dr Rajesh Agarwal said.
Chief Minister Yogi Adityanath has expressed profound grief over the demise of the Amapur MLA.
Singh, a resident of Hajipur village under Amapur police station, was a three-term MLA.
He is survived by his wife, two sons and a daughter.
On information about Singh's death, a large number of BJP leaders and workers, including local BJP MLA Vipin Verma David and Marhara MLA Virendra Lodhi, rushed to the hospital.
The party workers have alleged that a government ambulance was not provided for taking the MLA's body to his village.
They said the family had to arrange a private ambulance.
