| Honorific-Prefix: | Honourable |
| S. Nagarajah | |
| Honorific-Suffix: | MMC |
| Order1: | 11th |
| Office1: | Mayor of Jaffna |
| Term Start1: | 8 January 1966 |
| Term End1: | 24 March 1966 |
| Predecessor1: | S. S. Mahadeva |
| Successor1: | K. Ponnambalam |
| Birth Date: | 28 February 1931 |
| Death Place: | New Jersey, United States |
| Alma Mater: | Jaffna Hindu College Madras Christian College |
| Profession: | Lawyer |
| Blank1: | Ethnicity |
| Data1: | Sri Lankan Tamil |
Sinnathamby Nagarajah (28 February 1931 - 8 May 2008) was a Sri Lankan Tamil lawyer and Mayor of Jaffna.
Nagarajah was born on 28 February 1931.[1] He was educated at Jaffna Hindu College.[1] After school he went to the Madras Christian College from where he obtained a bachelor's degree and master's degree in English Literature.[1]
After returning to Ceylon Nagarajah worked as an attorney-at-law in the north and east of the country.[1]
Nagarajah was elected to Jaffna Municipal Council, serving as the city's mayor in 1966.[1] [2] He became vice-chairman of the newly created Jaffna District Development Council in 1981 but resigned in 1982.[1]
After the Indian Peace Keeping Force occupied Jaffna in 1989 Nagarajah moved to the Vanni with the rebel Liberation Tigers of Tamil Eelam (LTTE).[1] He taught at the LTTE's Tamil Eelam Judiciary Department.[1]
Nagarajah moved to New Jersey, USA in the 1990s and was active in the diaspora community.[1] He died on 8 May 2008 in New Jersey.[1]