Shri S. D. Sanjay was born into a modest family, the son of an educationist. He completed his schooling at Sir Ganesh Dutt Patliputra High School and went on to earn an Honours degree in Commerce from Vanijya Mahavidyalaya, Patna University, securing a First Class with distinction in Accounts. He thereafter moved to Delhi, where he obtained his LL.B. from the Campus Law Centre, University of Delhi and began his practice there. He returned to Patna within a year and commenced practice before the Patna High Court.
He set up his independent chambers in 1989, specializing in Constitutional Law, Civi, Criminal and Taxation law and within a few years had built a thriving practice in Patna. Leading one of the most highly regarded chambers at the Patna High Court, he was engaged by multiple corporate houses to represent them before the Patna High Court, the Jharkhand High Court, the Calcutta High Court, the Delhi High Court, and the Supreme Court of India. In the course of his practice, he has had the privilege of appearing alongside and against many of India's legal luminaries.
In 2010, Shri Sanjay was appointed Additional Advocate General for the State of Bihar, a position he held until 2014. In 2013, he was designated a Senior Advocate by the Full Court of the Patna High Court. He resigned as Additional Advocate General in January 2014 and returned to private practice.
In April 2015, the President of India appointed him Additional Solicitor General of India to represent the Government of India in the Patna High Court - a post created by the Government in December 2014. In that capacity he served as overal in-charge of the Union of India's litigation in Bihar and Jharkhand. He held the office until July 2020. Thereafter, he returned to private practice and developed lucrative practice in different fields.
In September 2024, Shri Sanjay was appointed Additional Solicitor General of India for the Supreme Court, New Delhi a recognition of his standing at the Bar and the breadth of his experience in the field of law. He has the distinction of appearing in high-stakes matters for the Government of India before the Supreme Court and various High Courts across the country. He represents the Government of India before Supreme court in an important matter concerning the establishment of Special Courts across the country for the expeditious trial of heinous offences. He also serves as Convenor of a committee constituted by the Supreme Court to frame a Standard Operating Procedure (SOP) on missing children and human trafficking for implementation across the country, interfacing with all the States. He has been appointed as the Convener of the Stock Witness Committee appointed by the Supreme Court for preparing standard operating procedure on stock witness for reform in criminal jurisprudence.
Shri Sanjay has long been associated with various social organisations. He is closely associated with the Dadhichi Dehdan Samiti an organisation dedicated to promoting awareness of eye, organ, and body donation and encourages people to pledge their support to the cause. He is also associated with the Bharat Vikas Viklang Nyas, which runs a hospital in Patna for the physically challenged.
On the family front, Shri Sanjay's wfe, Mrs. Sushila Agrawal, is also a lawyer. Their daughter Akanksha and son-in-law Dr. Siddarth Chaudhary are based in Silicon Valley, USA, while their son, Akshat, and daughter-in-law, Disha, are practicing advocates in the Supreme Court of India. His family has played an important role in his success.
He has been appointed as advocate General, Bihar with effect from 18-06-2026.