Kumar, who held the post of country's second highest law officer for over three years, has represented the Centre in the apex court in crucial cases including the pleas against demonetisation and rising pollution.
He is the second law officer to quit after Mukul Rohatgi, who had resigned as the Attorney General in June this year.
Kumar, a constitutional law expert, has assisted the apex court in deciding the issue whether a state government can grant pardon to the death row convicts in cases which are probed and prosecuted by central agencies like CBI. The issue had arisen out of the decision of the Tamil Nadu government to set free the killers of former Prime Minister Rajiv Gandhi.
The SG has said that he put in his papers as he was unable to attend to certain health issues of family members.
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"The government is good to me, but I tendered my resignation due to personal reasons," he said.
Kumar had succeeded SG Mohan Parasaran in 2014 after the Narendra Modi government assumed the office. His second term as solicitor general was renewed recently.
The office of Law Minister Ravi Shankar Prasad received his resignation letter today.
There was speculation a few months ago that the Supreme Court collegium was considering his name as a judge of the apex court.
Before assuming the office of solicitor general, Ranjit Kumar represented Gujarat government in several cases and assisted the apex court as amicus curiae in cases including the matter pertaining to Yamuna pollution.
Kumar had appeared in the the Sohrabuddin Sheikh encounter case and also represented then Tamil Nadu chief minister J Jayalalithaa in the disproportionate assets case in local Bangalore court.