He was the son of former Punjab Assembly Speaker and finance minister Kewal Krishan.
[3][4] Rajnish Kumar first unsuccessfully contested the Punjab Legislative Assembly elections in 2007 from Mukerian as a Congress candidate.
[5] During the 2012 Punjab assembly elections, Congress nominated Ajit Kumar Narang from Mukerian.
Rajnish Kumar decided to contest as an independent candidate, for which he was expelled from Congress.
[4][6] He successfully contested and became a member of the Punjab Legislative assembly by defeating 2nd placed BJP candidate Arunesh Kumar by more than 12 thousand votes.