The reshuffle is likely to see the inclusion of several young faces.
Information and Broadcasting Minister Ambika Soni and Tourism minister Subodh Kant Sahai on Saturday submitted their resignation to the prime minister.
Social Justice and Empowerment Mukul Wasnik also resigned from the Union Cabinet on Friday evening.
Earlier on Friday, Dr Singh accepted the resignation of External Affairs Minister SM Krishna, hours after the latter had forwarded his resignation in anticipation of Sunday's proposed reshuffle of the Union Cabinet.
Wasnik said after meeting Dr. Singh on Saturday: "I have already submitted my resignation to the prime minister on Friday evening."
These developments came as the prime minister met United Progressive Alliance chairperson Sonia Gandhi for a one-on-one meeting that reportedly discussed the Cabinet reshuffle.
Krishna said that he wanted to give a free hand to Prime Minister Singh during the reshuffle.
In recent times, Krishna has been dogged by several controversies, including a Lokayukta report against him and his decision to go to England to watch tennis matches at Wimbledon.
His resignation comes a day after a special Lokayukta court ordered its police to probe the involvement former Karnataka chief minister BS Yeddyurappa and Janata Dal-Secular leader HD Devegowda in the alleged Mysore-Bangalore Express Highway scam.
Meanwhile, the speculation over Congress General Secretary Rahul Gandhi joining the government continues.
Sources said Jyotiraditya Scindia and Sachin Pilot are among those likely to be elevated. The reshuffle could also involve some ministers caught in controversies like coal minister Sriprakash Jaiswal.
The Nationalist Congress Party has already said it will replace its minister Agatha Sangma. She is likely to be replaced by senior leader Tariq Anwar.