He started practice on Civil and Labour matters in the Madras High Court.
Ratnam became the member of the Executive Committee of the Tamil Nadu Legal Aid Board.
On 25 January 1979, he was appointed permanent Judge of Madras High Court.
[1] Since 15 November 1992, he also took charge of the Acting Chief Justice of Madras High Court.
[2][3] He also took charge in the post of Governor of Himachal Pradesh for 19 days.