Jeeva (Karthi) is a typical Chennai youngster. His father Pragasam (Jayaprakash), a call taxi driver, shows love and affection on him. They lead a simple life and derive happiness in whatever they do. One day, Jeeva comes across Priya (Kajal Aggarwal) at the wedding of their mutual friend. The two fall for each other. He doesn't tell her about his feelings and knows that she likes him. He plays hard to get until their mutual friend tells Priya about Jeeva's infatuation. Jeeva tries to make her become more independent. One day he goes up to Priya's father against her pleas and tells him of their love. Jeeva eventually secures a job as that is one of the requirements for him to marry Priya. Eventually Priya becomes acquainted with Jeeva's family and is accepted as the future bride.
When all seems to go well, a murder attempt on Jeeva’s father disturbs everything. Jeeva’s father had witnessed a girl being taken by a group of teenagers in his taxi. The girl is raped and killed. To get rid of the body of the girl and her boyfriend they hack both the bodies into small pieces and dumps them in random dump-yards in the city. When police accidentally recovers the head of the girl from a dumpyard, it is reported on TV. Jeeva's father suspects that the head recovered might belong to a girl who was taken by guys who boarded his taxi. So he decides to knock on the doors of justice and confirms to the police that the girl in his taxi and the murdered girl are the same. Sensing trouble, the gang plans to murder him as he has seen their faces. So they go to Pey Babu (Ramachandran Durairaj), the uncle of one of the teenagers, a local criminal who is adept at coming up with plans for murdering people. They conduct reconnaissance of Jeeva's father and their home. They also come to know about the upcoming marriage of Jeeva's sister when Pey Babu, under the guise of delivering a Pamphlet, takes a good look at Jeeva's family. Pey Babu assumes that Jeeva's family has to venture outside their home for wedding arrangements. The gang follows Jeeva's family to a wedding card shop where the gang hears the owner of the shop asking Jeeva and his father to come back in a couple of days to collect the printed cards. Now that Pey Babu knows the exact location and time of where Jeeva's father is going to be, he comes up with a detailed plan for murder. When Jeeva and his father return to the shop after two days, the gang starts a commotion in the crowded street and in the ensuing confusion, one of the gang stabs Jeeva's father with a piece of poisoned glass shrapnel.
During the murder Jeeva notices and identifies one of the Gang members as he looked like the same person that his father described during the previous investigation of the girl's Murder. The death of his father shatters Jeeva. The investigation of his father's murder brings the police to Jeeva's home where they ask him whether he had seen any suspicious person in his neighborhood in the days before his father's murder. Jeeva denies seeing any suspicious person although he later reveals to his friend that he indeed has seen a strange guy delivering pamphlets to his home and the guy during his father's murder. When his friend inquires why he did not say anything to the Police, Jeeva replies the guys do not deserve a police investigation and court trial. The heinous crime they committed, hacking a girl into pieces, deserves much harsher punishment. And he says that he is going to personally punish the gang not because they killed his father but because of the heinous and psychopathic nature of their crimes. He sets out on a mission to identify the culprits and goes running around the town baying for their blood.
Jeeva seeks the help of his friend Kutti Nadesan (Aruldoss), a Chennai gangster, who Jeeva got acquainted with in the past. Kutti Nadesan with his influence asks his gang to bring all the Guys who plans for murder in Chennai, so that Jeeva can identify him. It turns out there are only four people who can plan for murder in Chennai including Pey Babu. Nadesan interrogates the first person in front of Jeeva. The next is Pey Babu, but Jeeva gets distracted, but turns back just in time to look at Pey Babu and identifies him as the person who delivered Pamphlets to his home days before his dad's murder. Now a chase ensues and Jeeva successfully captures and subdues Pey. Now Jeeva coerces Pey into taking him to where the Teenage gang is. Both Pey and Jeeva goes to the road in front of the college where the five teenagers study. But before he can get hold of them, the gangs gets alerted and start a commotion by throwing cool drink bottles in the crowd. In the ensuing melee, Pey gets stabbed by one of the gang and Jeeva gets a clear look at the guy who stabbed Pey. So Jeeva chases him and beats him senseless . But the teenager is killed by a train when he tries to escape the clutches of Jeeva. Jeeva subsequently goes to the dead teenager's funeral hoping that his friends will come there. The gang arrives but sees Jeeva before he sees them .
They leave the funeral and to get drunk goes to one of the beaches which coincidentally is the same place Nadesan returns after going to the sea. The gang argues among themselves how their friend was killed by Jeeva and how they should avenge him. At the same time Jeeva calls Nadesan on his cell phone to use his influence to investigate about the friends of the Dead teenager. The gang while arguing starts shouting which distracts Nadesan and looking at them Nadesan asks Jeeva about the how the gang looks like. Sensing that Jeeva's description matches the gang on the beach, Nadesan goes to inquire them while giving the phone to another one of his group to give Jeeva, the directions to the beach. During the inquiry Nadesan confirms the Killers and the gang on the beach are the same but before he can do anything the gang clubs one of Nadesan's group and runs into a nearby area with dilapidated houses. Nadesan and two of his group grabs weapons and goes after them but they are killed easily as they are outnumbered by the four teenagers who hide and attack and finish them off one by one. Jeeva arrives just a few minutes late to see that Nadesan and his group slaughtered.
Now it is up to Jeeva to face four guys armed with blades and avenge his father's death. What follows is an intense, gut wrenching fight for survival between the gang and Jeeva. After a struggle Jeeva triumphs over the four rapists and buries them alive on the beach.
After his first feature film Vennila Kabadi Kuzhu, released in February 2009, became a success, receiving much critical acclaim as well, director Suseenthiran started to work on the script for his next film. Initially planning to do one titled Azhagarsamiyin Kudhirai, which failed to commence due to financial problems, he decided to first direct a film featuring a known lead actor, before coming back to that film. He was ready with the script by August 2009, revealing details about the project. While his previous work was based on sporting incidents in a rural background, this one was said to be a "total city subject", shot entirely in Chennai. An action family entertainer, it would deal about problems in city life, according to Suseenthiran. On 19 August 2009, it was announced that the film was titled Naan Mahaan Alla and would be produced by K. E. Gnanavelraja under the banner of Studio Green, who earlier had produced Surya's Sillunu Oru Kadhal and the award-winning Paruthiveeran by Ameer Sultan, which incidentally also starred Karthi in the lead role. It was reportedly based on a real-life incident that happened to one of the relatives of director Suseenthiran. He scripted the film for five months.
While Vennila Kabadi Kuzhu (Suseenthiran's first feature film) starred mostly newcomers, he chose Karthi for the lead role in this film as he felt that Karthi has an "innocence in his face" that was needed for this role and that he could "convey charm, innocence and being jolly at the same time". For the lead female role, Kajal Aggarwal, who had appeared in Tamil films as Pazhani, Saroja and Modhi Vilayadu, was roped in. Suseenthiran chose her after seeing her performances in the Telugu films Chandamama and Magadheera. He felt that her "cute expressions" were what he needed for that character. While Karthi's character is a middle-class bank employee, Aggarwal would play an employee in a mobile phone company.
Soori, who also played a comedic role in Vennila Kabadi Kuzhu was again included, while Jayaprakash, who played several supporting roles and rose to fame with his performance in Pasanga was chosen to play Karthi's father. As in his previous film, Suseenthiran introduced several new artists, such as five boys who played the villains with one of them being Vinod who played the younger character of Surya in Nandha. According to the director, he found three of them "loitering on a popular road in the city", whilst cinematographer Vijay Milton's assistant Ramachandran and cinematographer Aruldass debuted and played pivotal roles.
Filming began, after ten days of rehearsals, on 4 September 2009 and was held in cities as Chennai, Hyderabad and Visakhapatnam. In mid-September, reported locations included East Coast Road (ECR) near Chennai and later in the environs of the highways near Poonamallee in Chennai.
The soundtrack of Naan Mahaan Alla is composed by Yuvan Shankar Raja, making this his third collaboration with Karthi, after scoring highly successful results with Paruthiveeran (2007) and Paiyaa (2010), and his first with director Suseenthiran, who worked with V. Selvaganesh for his previous film. The soundtrack album, which was released on 16 July 2010 at Sathyam Cinemas, Chennai, features five songs, with lyrics penned by Na. Muthukumar and Yuga Bharathy. The song "Va Va Nilava Pudichi" is repeated at the end of the album, with singer Rahul Nambiar credited for both. Nambiar, however, stated on his Facebook site that two versions were recorded featuring his and Haricharan's voice, respectively, but that both songs in the album were rendered by Haricharan only and his own version wasn't included at all. The songs were later dubbed for the Telugu version Naa Peru Shiva. The Telugu album was launched on 25 June 2011.
Only three songs were used in the film in their entirety, with "Oru Maalai Neram" being left out completely. The album received favorable reviews, with "Iragai Pole" in particular, sung by composer Yuvan Shankar Raja, becoming very popular. Before the soundtrack release, Yuvan claimed on Twitter that the song was one of his favorites, on which he had worked for days. Interestingly, after seeing the entire film, he was said to have remixed and completely reworked that song, altering the orchestration inter alia, to match it with the visuals. He garnered accolades for the film's score as well. As per Suseenthiran, the music was "crucial" in the second half of the film, which was the reason for opting for Yuvan Shankar. According to Karthi, Yuvan had worked for 12 days for the score of the second half, which has "hardly any dialogues", adding that he was the one "who narrates the story in the second half through his music".
The satellite rights of the film were sold to Kalaignar. The film was given a "U/A" cerficate by the Indian Censor Board.
Naan Mahaan Alla received positive reviews, with Top10Cinema.com labelling Naan Mahaan Alla as "outstanding", proceeding to highlight that "almost everything works: the plot and screenplay, performances, technical panoramas", while Pavithra Srinivasan of Rediff.com described it as "almost perfect", giving it 3 out of 5. Sreedhar Pillai of Sify.com also gave a very positive verdict, stating that director Suseenthiran comes up with a "rocker of a film" that is "refreshingly fresh, innovative and packaged in a breezy manner within the commercial format", adding that it is "engrossing and racy". Furthermore, he praised lead actor Karthi's "power packed" performance, citing that he "nails the character to perfection" and "carries the film to its winning point". Similarly Times of India reviewer Bhama Devi Ravi, gave 3.5 out of 5, claiming the film to be "entertaining almost till the end", whilst addressing high praise to both Suseenthiran, who according to her is "turning out to be a treasure", and Karthi, whose performance she described as his "best work yet". Behindwoods gave the movie 2.5 out of 5 and said "Although there are a few slow patches, Suseendiran should be appreciated for coalescing the energy and entertainment of a mainstream film with a sensitivity of a realistic one. He has the wholesome attention of the audience in most parts."
The film opened well, and made a steady progress in the Chennai box office, eventually becoming a very successful venture. In five weeks Naan Mahaan Alla made a collection of ₹ 5 crore; 4.47 crore was collected in Chennai city alone.