During his tenure, Gupta was involved in numerous high-profile cases, witnessing the execution of several inmates including the notorious Ranga and Billa, and Afzal Guru, involved in the 2001 Indian Parliament attack. His experiences and observations led him to significant contributions in prison reform; he played a key role in drafting the Delhi Prison Act and Manual in 1988, established Tihar's first legal aid cell, and initiated special court sessions within the prison to expedite minor cases.

Post-retirement, Gupta transitioned into law, practicing at the Supreme Court of India and the Delhi High Court.

His memoir, "Black Warrant: Confessions of a Tihar Jailer," co-authored with journalist Sunetra Choudhury, became the basis for a Netflix series, shedding light on the inner workings of India's prison system. Gupta's career not only highlighted the systemic issues within Indian prisons but also his commitment to reform and humane treatment of inmates.