Viswanathan, a former Additional Solicitor General, has been in the profession for more than 30 years and has appeared in a number of high profile matters.

Coming from a family of lawyers, he attended the Law College at Coimbatore in the first batch of the five year course that graduated in 1988. During the entirety of the five years, he attended the chambers of advocate KA Ramachandran, a criminal trial lawyer at Coimbatore.

After enrolment, he moved to New Delhi and joined the chambers of Senior Advocate CS Vaidyanathan who subsequently served as an Additional Solicitor General of India.

In 1990, he moved to the chambers of Senior Advocate KK Venugopal who later became the Attorney General for India

Viswanathan worked there for nearly 5 years.

In April 2009, he was designated as Senior Advocate by the Supreme court.

Speaking to Bar & Bench in 2014, Viswanathan spoke of the need to include criteria like minimum number of reported judgments and pro bono work undertaken for the selection of judges to the higher judiciary.

"The amount of income tax being paid alone cannot be the basis. Experts in fields like criminal law and taxation also have to be considered. There has to be diversity. In England, some men of Asian origin have been appointed. Mr. Rabindra Singh has been appointed at the age of forty seven as a High Court judge which is commendable. Apart from merit, they look at diversity. We also need to consider that because we are a diverse society", he had said

Central government notifies appointment of Justice TS Sivagnanam as Acting Chief Justice of Calcutta High Court