The RLD chief, a prominent leader in western Uttar Pradesh, was admitted to a private hospital in Gurugram after his condition deteriorated due to a lung infection on Tuesday.
Ajit Singh had tested positive for the novel coronavirus on April 20.
The son of former Prime Minister Chaudhary Charan Singh, Chaudhary Ajit Singh was a seven-time MP from Baghpat. He also served as the Union Minister of Civil Aviation.
An alumnus of the Indian Institute of Technology, Kharagpur and Illinois Institute of Technology, Chicago, Ajit Singh was first elected to Rajya Sabha in 1986.
Ajit Singh forayed from Lok Dal to Congress and allied with the Bharatiya Janata Party (BJP) and Samajwadi Party.