Ajith was born on 1 May 1971, in Hyderabad, India. His father P.Subramaniam is from Chennai, Tamil Nadu. His mother Mohini is from Kolkata, West Bengal. Ajith created the non-profit organisation "Mohini-Mani Foundation", named after his parents, in order to promote self-hygiene and civic consciousness and to help ease the problems of urban sprawl. Ajith was the middle son out of three brothers, the others being Anoop Kumar, a stockbroker in New York, and Anil Kumar, an IIT Madras graduate working in Seattle. Ajith also had younger twin sisters, both of whom died young.
Ajith did not speak Tamil as a child, and mastered it only after becoming an actor. He dropped out of Asan Memorial Senior Secondary School in 1986 before completing his higher secondary. During his childhood he had been a fan of M. G. Ramachandran, Amitabh Bachchan & Rajesh Khanna. In his teenage, he became a fan of Tamil acting icons, Rajnikanth & Kamal Haasan. At 18, Ajith had to take up a job to support his career in racing. Joining as an apprentice, he rose to be a merchandiser with a garment export company, doing small-time press ads and TV commercials occasionally. He had put a lot of money into racing and would borrow tyres from his friends who used to help when the chains wore out, as there was no money in racing at that time. Following an accident, several business agencies pushed him into modelling for advertisements in print media. He had to make a choice between films and racing, and as the films were happening and generating him some money, he began concentrating on it. He debuted in En Veedu En Kanavar (1990) in a minor role as a school student.
Aged 20, Ajith was selected by a Telugu film production company, Lakshmi Productions, to star in its film; however, shooting was stalled soon after filming began, following the death of the film's director. Ajith then started his film career at the age of 21 appearing in the low budget Telugu film, Prema Pustakam in 1992, which remains his last direct Telugu film to date. His first Tamil film Amaravathi, directed by then newcomer Selva, was a moderate success and his voice was rendered by fellow actor Vikram. After the release and while training for an amateur motor race, Ajith suffered a fall, injuring his back and underwent three major surgeries resulting in a bed rest for one and a half years. Following the injury in 1993, Ajith played a small role in the Arvind Swamy starrer, Paasamalargal, before appearing in a supporting lead role in the family drama, Pavithra, which featured him as an ailing patient shown maternal affection from Raadhika.
In 1995, after making a guest appearance in the Vijay starrer Rajavin Parvaiyile, Ajith appeared in his first major success Aasai. The film, directed by Vasanth and produced by Mani Ratnam, featured him in the lead role opposite Suvalakshmi, whose brother-in-law infatuates about her. The film became a big success and established Ajith as an upcoming actor in the Tamil film industry. He later played the lead in Kalloori Vaasal co-starring Prashanth and Pooja Bhatt. Ajith's second successful film came in the form of National Award winning Kadhal Kottai, in which Ajith reunited with Agathiyan, the director of the earlier project Vaanmathi, the film which told the tale of two people falling in unconditional love without seeing each other until the climax. The film paired him opposite Devayani, with Heera Rajgopal playing a supporting role. Heera, Ajith's then girlfriend, played a major role in shaping Ajith's career.
After the success of his films in 1996, the following year saw a series of five classical success, one such being Amitabh Bachchan's Tamil production Ullaasam with Maheswari, in which he was paid a salary of ₹2 million (equivalent to ₹7.7 million or US$120,000 in 2016) for the first time. Ajith returned in 1998 with another big, successful project in Saran's Kaadhal Mannan, a "masala film" setting the foundations for an expanding fan base. He also began acting in Vasanth's Nerukku Ner, and was later replaced by Suriya. Following films Aval Varuvala and Unnidathil Ennai Koduthen also became successes, with the latter featuring Ajith in a guest role. Except for Uyirodu Uyiraga which performed poorly, his other 3 films released in 1998 and 6 in 1999 were box-office hits. Ramesh Khanna's Thodarum, Sundar C's romantic drama Unnaithedi opposite Malavika set the tone for a series of big successes.
S. J. Suryaah's thriller, Vaali, which portrayed him in dual roles for the first time opposite Simran, became one of his biggest hits during the time. The film told the story of a deaf and mute brother setting his eyes on his younger brother's wife, with Ajith's portrayal of the two brothers winning him his first of many awards for Filmfare's Best Actor. Furthermore, Ajith's portrayal of the brothers was also praised, with critics claiming that the film was an "instant classic" with Ajith showing that he is a "talented actor". The two following supporting roles in the drama films Anandha Poongatre and Nee Varuvai Ena also brought Ajith plaudits for his portrayals. His final film before the new millennium was Amarkalam, directed by Saran and featuring Shalini, whom he married shortly after the film. Amarkalam told the story of a negelected child who grew up and fails to show feelings of love or affection, becoming a gangster in the process, with Ajith's depiction of his rogue character appreciated by critics.
His next, Mugavaree, won him commercial and critical praise. The film revolved around the life of a struggling music composer who faces sacrifices to proceed in his career. The film featured dual endings, one with Ajith succeeding in his career, the other with Ajith dejected. Ajith's performance was yet again praised with critics from Rediff, claiming that "Ajith is the real winner", drawing an allusion with the film's script, whilst adding that "it is amazing to see how Ajith has grown as an actor. He brilliantly portrays the vulnerable and sad Sridhar". He also appeared in A. R. Rahman's 2000 musical Kandukondain Kandukondain directed by Rajiv Menon. The film featured Ajith alongside prominent actor Mammooty and actresses Aishwarya Rai, Tabu and Srividya. In a similar role to his previous film, Ajith played a struggling film director facing an oscillating relationship with Tabu, with the pair being unanimously praised for their roles. After giving 6 straight hits in 1999 and having had Mugavaree and Kandukondain Kandukondain in 2000 as success, Ajith had an unsuccessful film, Unnai Kodu Ennai Tharuven co-starring Simran.
In 2001, Ajith appeared in 3 commercially successful Tamil films. Dheena, A. R. Murugadoss's debut film co-starring Laila Mehdin and Suresh Gopi, indirectly marked the beginning of a new image of Ajith that of an action hero that would appeal to the masses. Furthermore, Ajith's nickname in the film, Thala, Tamil for Leader, became a new identity for the actor amongst his fans. In the same year, he was offered a role in Nandha, which he rejected. His next was the much-hyped thriller, Citizen, portraying him in ten different get-ups and it became a commercial success at the box office. A role in the family drama Poovellam Un Vasam followed opposite Jyothika and was a success commercially and critically earning a Special Best Actor Award from the Tamil Nadu State. The year ended off with an appearance in Santosh Sivan's Hindi project, Asoka, in which Ajith appeared in a brief negative role alongside Shah Rukh Khan, which did not perform well. In 2002, Ajith appeared in three films, the first two, Red and Raja, being box office disappointments, the former further building up his image as an action hero. The third film, Villain, in which Ajith appeared in dual roles, one as a mentally ill person, became successful and earned his second Filmfare Best Tamil Actor Award.
From 2003 through 2005, Ajith appeared in fewer films due to his career in motor racing becoming more prominent. 2003 saw the release of his long-delayed Ennai Thalatta Varuvala and the police drama Anjaneya, both failing commercially. In that period, three films, namely Saamy, Kaakha Kaakha and Ghajini, were turned away by the actor due to various reasons.
His next film, Jana with Sneha, also became a big failure, with the Saran film, Attagasam, being his only hit in the period. The film, saw Ajith portray dual roles, with a song, "Thala Deepavali", penned to promote his action image. In 2005, the failure of the Linguswamy film Ji, despite garnering positive reviews and taking a strong opening, saw Ajith take a sabbatical from acting to re-work his image. Of the five films released between 2003 and 2005, his only box-office hit was Attagasam.
During 2006, Ajith returned from his hiatus by appearing in P. Vasu's Paramasivan for which he had lost twenty kilograms to portray the lead role. The film enjoyed a moderate success, scoring over Vijay's Aadhi, which also released in the same week, at the box-office. Critics from The Hindu stated Ajith looked "trim and taut" in the film with "only his eyes seeming to have lost some of its sparkle", following the major weight loss. Furthermore, for Paramasivan and his two other projects in 2006, Ajith sported long hair, which was being grown for Bala's project, Naan Kadavul, which Ajith eventually opted out of. Similarly his next, AVM Productions's, Thirupathi directed by Perarasu performed above average business at the box-office, despite garnering poor reviews, with Rediff critics citing that the film is "anything but sensible" but that Ajith "salvages the situation with a spirited performance". Ajith summed up a successful comeback by the release of his long-delayed film Varalaru, which went on to become his biggest success til date. The K. S. Ravikumar film co-starring Asin, portrayed Ajith in three roles, including that of a classical dancer, with his portrayals being critically praised. Moreover, the film earned Ajith his third Filmfare Best Actor Award. In 2007, media reports hinted that the actor would do a project with Shankar. Ajith's first release in 2007, Aalwar, became a debacle at the box-office, with his previous film still continuing to run in theatres even after Aalwar had stopped its brief theatrical run. Kireedam, a remake of the 1989 National Award winning Malayalam film of the same name, was released to positive reviews, with the film also becoming a moderate success. During the shoot of the film, Ajith developed a further spinal injury, a recurrence of his problem earlier in his career.
Ajith then starred in Billa, a remake of the 1980 Rajinikanth starrer of the same name. The Vishnuvardhan directorial fetched critical praise for Ajith, becoming a trend-setter for stylish art direction and cinematography in India. Billa, yet again, featured Ajith in dual roles, one of a notorious don whilst the other played an innocent person who had to act as the don, following the former's death. After Billa, Ajith appeared in the film Ayngaran International production Aegan, directed by the choreographer turned director Raju Sundaram. The film, a remake of the 2004 Hindi comedy Main Hoon Na, failed at the box office.
Following a year of production, Ajith's Aasal released in February 2010, taking a grand opening at the box office. The film, which also featured Ajith in dual roles, also failed at the box office despite its bigger expectations.
After a second foray into motor racing, Ajith signed a film directed by Venkat Prabhu, titled Mankatha, which notably became his 50th project. The film featured him in a full-length negative role as Vinayak Mahadevan, a suspended police officer who lusts after money. His performance and his decision to portray a character with negative shades, breaking the stereotype hero image in Tamil cinema, were lauded by critics, with reviewers from Sify and Rediff terming the film as an "out and out Ajith film" that worked "only because of Ajith". Heaping praise on the actor's performance, the former noted that he "rocks as the man with ice in his veins as the mean and diabolic cop" and that he played "the emotionless bad man, to perfection", while the latter wrote that he had "carried practically the whole film on his capable shoulders". Mankatha became a financially successful venture.
Ajith then starred in Billa II, a sequel to his 2007 film Billa, which released on 13 July 2012. Reviewers appreciated Ajith's screen presence and stunts and blamed him for the choice of story and the director. Eventually, the movie performed poorly at the box-office. He has starred in Vishnuvardhan's Arrambam alongside Arya, Nayantara and Rana, which was released on 31 October, and earned positive reviews from both critics and audience. His next film post Arrambam was Veeram directed by Siva co-starring Tamannaah, which was released on Pongal 2014, which also earned positive reviews from critics. Ajith's next film was Yennai Arindhaal, with Gautham Menon as director. Ajith's performance as Sathyadev IPS was widely praised with a critic calling it "Ajith's best since Kandukondain Kandukondain". Ajith was subsequently nominated for the Filmfare Award for Best Actor – Tamil in the 63rd Filmfare Awards South. Ajith worked with Siva again in Vedalam (2015), in which critics praised his performance. His latest project is Vivegam.
In 2004, Ajith was signed as Nescafe's brand ambassador in Tamil Nadu. Later, he has limited his appearance to the silver screen by not appearing or promoting any commercials.
Ajith became a race car driver, competing in circuits around India in places such as Mumbai, Chennai and Delhi. He is one among very few Indians to race in International arena and in Formula championships. He has also been abroad for various races, including Germany and Malaysia. He drove in the 2003 Formula Asia BMW Championships. He raced in the 2010 Formula 2 Championship along with two other Indians, Armaan Ebrahim and Parthiva Sureshwaren.
After a one-off race during the Formula Maruti Indian Championships in 2002, where he finished in fourth place, Ajith signed a contract with manager Akbar Ebrahim confirming his participation in the inaugural Formula BMW Asia Championship. Despite spinning out in the first lap of his first race, Ajith successfully completed the season by finishing twelfth.
After a six-year sabbatical, Ajith signed up for his third season of car racing by participating in the 2010 season of the FIA Formula Two Championship. The decision to be involved in the sport was made after Ajith's film directed by Gautham Menon was delayed, allowing him to participate in the whole season. Prior to signing up, he competed in the final round of the MRF racing series in Chennai in February 2010, but failed to finish the race due to mechanical problems. Further trials in Sepang, Malaysia followed suit as he practised for the season's beginning in April 2010 in his Formula Renault V6 car with Eurasian Racing, shedding 11 kilograms during training.
In 1999, during the shoot of Saran's Amarkalam, Ajith began to date his co-star Shalini. At that time, their involvement made him a regular subject of tabloid gossip, a role to which he was accustomed following his previous relationship. He proposed to Shalini in June 1999, and following consultations with her family, she agreed. They were married in April 2000 in Chennai. On 3 January 2008, their daughter, Anoushka, was born in Chennai. On 2 March 2015, their second child, a son Aadvik was born. Through his marriage to actress Shalini, he became brother-in-law to actor Richard Rishi, and actress Shamili, who appeared as his sister-in-law in Rajiv Menon's Kandukondain Kandukondain.