Justice SN Aggarwal joined the Punjab judicial service in 1972. He saw various postings in Punjab. Upon selection by the UPSC, he also remained posted as Law Secretary in the Andaman & Nicobar Administration at Port Blair. He got elevated as a Judge, Punjab and Haryana High Court in 2004.

Justice Aggarwal belongs to a family of freedom fighters and that infused in him the script to wrote the book 'The Hero of Cellular Jail', documenting the sacrifices of revolutionary patriots who suffered numerous tortures in Cellular Jain in Port Blair for India's freedom. NCERT adopted this book as a dream project and published it in concise form in 2011 as 'The Cellular Jail in our Freedom Struggle' as supplementary reading for senior secondary students. Justice Aggarwal has also written five well-received books on law.