There is not a very clear cut picture about the exact time period of when the temple was built or who exactly built it. However, there is a prominent legend behind the same. There once lived a Markandeya Maharishi who was a staunch devotee of Lord Vishnu. He prayed to the Lord to bless him with a daughter. Deeply pleased with his devotion the Lord granted him the wish and one day the Maharishi found a small two year girl child playing under a Tulasi tree in the Thirunageswaram forest. The Maharishi thanked Lord Vishnu and brought her home. After a few years, Lord Vishnu came to his house in the form of an old Brahmin. He asked the hand of his daughter for marriage. However, the Maharishi explained to him that his daughter was too young for marriage. The Brahmin did not listen and was adamant about his decision. He even proclaimed to die if he was unable to marry the girl. The girl on the other hand also became very upset and started crying as a mark to avoid this marriage. Fixed at what to do, the Maharishi prayed to Lord Vishnu to show him a path. As soon as he opened his eyes, he saw Lord Vishnu in his original form, holding the hands of his daughter. He was amazed at this and readily agreed to marry off his daughter. Since, that time Tirunageshwaram has been considered as a sacred spot.