Mr Kumar had been a counsel for the Gujarat government and amicus curiae in several cases in the Supreme Court. Among the cases he represented were the Sohrabuddin Sheikh encounter case.
Recently, he appeared before the Supreme Court on behalf of the family of a woman, who was at the centre of 'snoopgate' controversy in which the the Gujarat Chief Minister Narendra Modi's name had figured.
Mr Kumar had also represented Tamil Nadu Chief Minister Jayalalithaa in the disproportionate assets case pending in a Bangalore court.
Sources said more law officers are likely to be appointed in the coming days.
G E Vahanvati and Mohan Parasaran resigned last week as Attorney General and Solicitor General respectively along with other law officers after the NDA government assumed office.
It is a convention that law officers step down with the change of government.
The previous UPA-II government had appointed 12 Additional Solicitors General.
