His father adopted Arya Samaj in Sonipat and worked as a teacher and was renowned as Master Hazara Singh.

[citation needed] Singh's political journey started with Sanjay Gandhi in Indian Youth Congress.

He lost to Jasbir Mallour of INLD in the 2000 Assembly election but regained the seat in 2005.

In 2019, he contested from Kurukshetra Lok Sabha constituency as a Congress candidate but lost after polling 3.48 lakh votes.

In 2024 Haryana Assembly Election Nirmal Singh won the Ambala City seat from BJP candidate Aseem Goel.

[18][19][20] In December 2023, he and his daughter Chitra resigned from AAP and are likely to join the Congress party again in January 2024.

[21] In October 1994, he was implicated in a murder investigation and he voluntarily resigned as a Minister of State for Revenue.