Karunanidhi was in poor health from October 2016 and minimised his political activities and public appearances, with the last one being on his 94th birthday on 3 June 2018.
On 28 July 2018, Karunanidhi's health deteriorated and became "extremely critical and unstable", and he was admitted at Kauvery Hospital in Chennai for treatment. He died there at 6:10 p.m. on 7 August 2018 due to age-related illness, which led to multiple organ failure.
The government of Tamil Nadu declared a public holiday on 8 August 2018 and a seven-day mourning after Karunanidhi's death.
A national mourning on 8 August 2018 was announced by the government of India. The national flag flew half-mast in Delhi, all state capitals and across Tamil Nadu on 8 August 2018.