Ramanthapuram District has an area of 4123 km², and a population of 1,183,321 (as of 2001). It is bounded on the north by Sivaganga District, on the northeast by Pudukkottai District, on the east by the Palk Strait, on the south by the Gulf of Mannar, on the west by Thoothukudi District, and on the northwest by Virudhunagar District.

The district contains the Indian portion of Rama's Bridge, an east-west chain of low islands and shallow reefs that extend between India and the island nation of Sri Lanka, and separate the Palk Strait from the Gulf of Mannar. The Palk Strait is presently navigable only by shallow-draft vessels.