Kayamkulam was a medieval feudal kingdom, known as odanadu, ruled by the Kayamkulam Rajas, with their royal palaces at Eruva and Krishnapuram. Maha raja Marthanda Varma (1706–58) conquered kayamkulam and annexed its territories to Travancore. It is said that the kingdom of Kayamkulam had a huge army led by a valiant commander Yeruvayil Achutha Warrier and therefore the large army of Travancore attempted three times before they succeeded in capturing Kayamkulam. The present day palace was built in its place by Marthanda Varma after he annexed Kayamkulam to Travancore. Kayamkulam, Mavelikkara and Karunagappally were previously known as Onattukara. Kayamkulam had slave markets in the 17th century.

The Krishnapuram Palace, built in the 18th century, now functions as a museum. Constructed in typical Kerala-style architecture, it has the largest mural painting in Kerala. Also, this palace museum at Krishnapuram houses the famous Kayamkulam double-edged sword. Cartoonist Sankar Memorial National Cartoon Museum and Art Gallery, is the first of its kind in the state and would be elevated to the ‘top cartoon study centre’ in the country. Kayamkulam Lake is a part of the Kerala backwaters tourist map. The Kayamkulam Boat Race is held on the fourth Saturday of August every year. The famous Chinese fishing nets can be found on the banks of the lagoon. Azhikkal Beach (Aayiram Tengu) and Valiya Azhikkal beach (Kochiyude Jetty) have gained popularity as tourist locations.