Modi said he was saddened beyond words at his demise.
Singh was firmly rooted in Indian values and took pride in its centuries-old traditions, he said and lauded him as a “statesman, veteran administrator, grassroots level leader and great human”.
He leaves behind an indelible contribution towards the development of Uttar Pradesh, the prime minister said.
“Kalyan Singh Ji gave voice to crores of people belonging to the marginalised sections of society. He made numerous efforts towards the empowerment of farmers, youngsters and women,” he said.
Singh (89), who had been ailing for some time, breathed his last on Saturday night, the Sanjay Gandhi Post Graduate Institute of Medical Sciences (SGPGI) in Lucknow said.
Singh was closely associated with the Ram Janmabhoomi movement.
The Babri mosque in Ayodhya was demolished when he was the state’s chief minister in 1992.
The Supreme Court had in 2019 handed over the disputed site to Hindu bodies, paving the way for the beginning of the construction of Ram temple there.
A backward caste leader, Singh was instrumental in the rise of the BJP to power in Uttar Pradesh in 1990s.