Presiding deity Lord Adi Varaha
The 9-foot high Lord's idol (immovable) has His consort Akhilavalli Ammal seated on His left thigh, His left hand encircling Her waist, Her feet resting on the Lord's lower palm. ("Ida" in the name "Thiruvidanathai" refers to the Lord holding His consort on His left side. "Ida" means "left side"). Lord is holding a conch in His upraised right hand and discus in His left. His right foot, raised knee-high, is resting on the many-hooded serpent Adi Sesha.

The Utsavamurthy (procession deity) is Nithya Kalyana Perumal, invariably dressed as a bridegroom, with a black spot (to ward off evil eye for the groom) on His left cheek. Marriage ceremony is conducted everyday and so the Lord is fondly called as "Nithya Kalyana Perumal" ("Nithya" means daily and "Kalyana" the marriage).

Mythology associated with Thiruvidanthai
The temple is rich is puranic lore. Once upon a time, there lived a sage, Kalava by name, who had 360 daughters. In those days, this temple town was so huge that it had 360 agraharams (main streets). Out of respect for the sage, residents in each street took up the task of bringing up each of the 360 daughters of the sage. When they grew up, the sage thought that it would be a Herculean task to get them all married suitably; praying fervently, he took refuge at the feet of Lord Adi Varaha. The most compassionate Lord Maha Vishnu assumed the form of a Brahmachari (bachelor), appeared in the first agraharam, proposed marriage with the first daughter and then married her. When the newly-weds visited the temple of Lord Adi Varaha, they vanished mysteriously in the sanctum sanctorum. This was repeated to the rest of sage Kalava's daughters, day after day. The bewildered Maharshi wanted to know from God Himself the whereabouts of his daughters and sons-in-law. When he entered the sanctum sanctorum, Lord Varaha appeared before him, holding all the 360 daughters on His lap. The Lord merged all the 360 souls into the single soul of Goddess Lakshmi, making Her sit on His raised left thigh. The sage was greatly elated to be the father of Goddess Lakshmi Herself. As the marriage ceremony continued day after day for 360 days, the place came to be known as "Nithya Kalyana Puri" and the lord as "Nirthya Kalyana Perumal". Vaishnavite philosophy speaks of the whole mankind as female and Lord Maha Vishnu as the only male "Purushothama". Eternal union of the souls with the God brings salvation (Jeevatma merging with Paramatma). A great truth is driven home symbolically as the merger of the brides and the bridegroom. On the earthly level, it is believed that worship of this Lord confers bliss of marriage faster.

Mythology says that Lord Sri Adi Varaha helped Lord Srinivasa in Tirupathi, by giving the land. As to explain this, we can find a big white bindhi(big dot) in the chin of Lord Nithya Kalyana Perumal and the Goddess, as seen in the deities of Tirupathi.

Noted Vaishnavite saint of yore, Thirumangai Azhwar, has sung in praise of the Lord at Thiruvidanthai. The Lord here is said to have appeared before Markandeyar, the immortal sage.

History
Epigraphical evidences found in the temple speak of Kings belonging to different dynasties like Chola, Udaiyar, Pandya, and others. Patronizing the temple from the 10^th to the 16^th centuries A.D. On festive occasions, the deity is decorated with a garland of 108 Saligrams, which was presented to the Lord by a staunch devotee Hariseka Maharaj, the ruling chief of Mahabalipuram.

Temple Premises
The sacred shrine faces the sea on the East. Surrounding the sanctum sanctorum, there are small separate shrines for Komalavalli Thayar (the first daughter of sage Kalava), Sri Andal, Lord Ranganatha, Goddess Ranganayaki and others. The holy water-front are Kalyana Theertham and Varaha Theertham. Holy dips in these sacred tanks during the solar months of Aries (April-May) and Aquarius (February-March) respectively would ensure wish-fulfilment and salvation. There is also another sacred water-front called "Ranganathar Theertham".

Special days of worship
Large crowds throng the temple for worship on the days of Vaikunta Ekadasi. The annual festival is celebrated with much pomp and splendour on the day of star Pushya in the solar month of Capricorn (January-February). The deity is taken on a procession in a palanquin, exquisitely carved with ivory images, depicting the ten incarnations of Lord Maha Vishnu.

During the solar month of Pisces (March-April), a 9-day festival "Panguni Uththiram" is celebrated. The day of the star "Uttara Phalguni" assumes significance.

Special worship for speedy wedlock
At the temple, special poojas are conducted for those aspiring marriage. The aspirant is to perform archana and offer two garlands to the Lord Adi Varaha and the Goddess. The aspirant is asked to wear a garland then and circumambulate the temple precincts nine times, devoutly praying to the Lord for happy, speedy wedlock. Garlands of the deities are then distributed to the aspirant, asking him / her to safeguard them in the pooja room, till the marriage materializes. After the marriage, dried garlands are to be returned to the temple by the happy newly-wed couple. There stands a huge tree as testimony, holding thousands of dried garlands, after fulfilling the wishes of speedy wedlock to many a devotee. For Rahu-Ketu afflictions in the horoscope, special worship is offered here to the many-hooded serpent Adi Sesh Nag, which holds the divine feet of the Lord of Thiruvidanthai.