[4][5] Shanmugam has also received praise for being one of the top cross-examiners in Singapore and has acted for and against all three prime ministers in civil lawsuits.

During his time in law school, Shanmugam earned several awards, book prizes and scholarships for being the top student from his first to third years and for academic merit (1982–1983).

[8] After being admitted to the Singapore Bar as an advocate and solicitor in 1985, Shanmugam went into private practice and became a senior partner and Head of Litigation and Dispute Resolution at Allen & Gledhill.

In 1995, the International Herald Tribune selected Shanmugam to represent them after the Lees and Goh initiated a civil libel lawsuit against the newspaper.

[10] At the age of 29, Shanmugam entered politics when he joined the People's Action Party (PAP) team contesting in Sembawang GRC in the 1988 general election.

The PAP team won and Shanmugam was elected the Member of Parliament representing the Chong Pang division of Sembawang GRC.

[12] As of 2015, Shanmugam remains as a Member of Parliament representing Chong Pang ward, which had become part of Nee Soon GRC.

During the public hearings, he questioned Simon Milner, Facebook's Vice President of Public Policy for Asia-Pacific, about the misuse of online data by Cambridge Analytica., and crossed swords with historian Thum Ping Tjin over a paper about Operation Coldstore written by Thum in 2013.

He has met Pope Francis in the Vatican City and has referred to the Pontiff as exemplifying the "essence of religion" and a "strong advocate of interfaith dialogue and understanding".