Sathya(Sathyaraj), an extra in movies, becomes a hero by poisoning the director's mind against the original hero(Ramesh Khanna). Cunningly manipulating his heroine Nandhita(Mumtaj) and then a leading heroine Aishwarya(Namitha), he soon becomes a top hero in Kodambakkam. Meanwhile, the Chief Minister(Manickavinayagam) has quit following his involvement in the bonds scandal and wants to appoint his own son as his successor. Arivanandam(P.Vasu), his second-in-command, who has been eyeing the CM post, splits and starts a new party. Seeing Sathya's popularity, Arivanandam requests him to join his party and this paves the way for Sathya's entry into politics.

Since it straddles both movies and politics, actors who are being seen as potential politicians naturally bear the brunt of the jokes. Rajnikanth is hardest hit as everything, from his eulogisation in movies to his comments before casting his vote at the last elections, is torn apart. And every actor who has vacillated about his entry into politics is sure to cringe when Satyaraj comments on the reasons behind this. But while these make us admire its daring and satire, its when Mahaanadigan spoofs other movies(like the Autograph reference when Ramesh Khanna returns to the studios) that the movie is at its funniest. Unfortunately, such moments take a backseat to jabs at other people, which make it seem a little mean-spirited.

But Mahaanadigan is at its most daring when it deals with politics. When even Kamalhaasan had to bow down to political pressure and rename his movie as Virumaandi , it seems quite brave of Satyaraj to pointedly ask a politician in the movie not to ask actors to rename movies. Karunanidhi's overacting during his early morning arrest is also recreated, though there are no obvious shots at the current administration. At the same time serious events are given their due with the script pulling no punches when pointing to the reasons behind the tragic school fire in Kumbakonam.

While the script usually supports the story in a movie, Mahaanadigan feels like its story was built around its script. While the dialogs and events refer to current events, the story itself is so unbelievable that the movie frequently feels like a fantasy rather than a satire. As Satyaraj turns into a hero after a single conversation with the director or walks around on his own after becoming an important politician, we realise that realism is not high on the director's list of objectives. The climax is Utopian though like Mudhalvan , it does leave us wishing that it would really happen.

Satyaraj has obviously enjoyed himself in the role and at the same time, its hard to imagine any other actor(maybe with the exception of Parthiban) carrying off the sarcastic lines with the same effect. The characters like MGR, Rathakkanneer M.R.Radha, Hitler and Jesus that he wears briefly during a song sequence sit quite well on him too. Namitha and a slimmed down Mumtaj have little to do. Directors litter the screen with P.vasu and Rajkapoor playing the usual bad guy routines. Deva keeps his reputation intact with not a single tune being memorable.