The film stars Vijay in triple roles, alongside S. J. Suryah, Kajal Aggarwal, Samantha Ruth Prabhu and Nithya Menen.

The film follows two brothers who were separated after the younger one's birth; Vetri, a vigilante magician who is against the medical crimes and Maaran, a reputed doctor who charges meagre amounts from his patients.

The film received mostly positive reviews with critics praising the performances of Vijay, Menen and S. J. Suryah, A. R. Rahman's soundtrack, cinematography, social message and Atlee's direction, but criticised the cliched plot and excessive length.

Maaran explains that the four were responsible for the death of an auto driver's daughter and the subsequent suicide of his wife due to their greed for money and negligence in providing proper healthcare.

He gives Randy the locations of his hostages but asserts that if they reach the hospital in time, then they will survive, like the auto driver's daughter.

Daniel Arokiaraj, another corrupt doctor and the head of the state's medical council, saw Maaran's inexpensive healthcare as a threat to his flourishing hospital business.

Before leaving, Vetri gives a press conference justifying his actions by exposing corrupt medical practices and the embezzlement of money in the field.

[20] In October 2016, Safwan Saleem, the chief executive officer of the production house, confirmed the project; and further announced that writer V. Vijayendra Prasad, who had earlier worked in films like the Baahubali series and Bajrangi Bhaijaan will be a part of the technical team.

He learnt the magic tricks from three magicians: Gogo Requiem from the Republic of Macedonia,[25] Raman Sharma from Canada,[26] and Dani Belev from Bulgaria.

[36][37][a] However, the production team later revealed that Jyothika opted out of the film due to unavoidable reasons and the role went to Nithya Menen in her first collaboration with Vijay.

[38] In January 2017, A. R. Rahman was reported to compose the film's background score and soundtrack album, collaborating with Vijay after ten years since Azhagiya Thamizh Magan (2007).

[60] The team has decided to shoot with Vijay and Nithya Menen in Jaisalmer for a song (which was later titled as "Aalaporaan Thamizhan"), irrespective of the hot weather prevailing in the location.

"[82] A. R. Rahman composed the soundtrack album and background score of Mersal, teaming up with Vijay for the third time, after his films Udhaya (2004), and Azhagiya Tamizh Magan (2007), and his first collaboration with Atlee.

[91][92] As an innovative approach, Hema Rukmani teamed up with ICONICbot, an Indo-Austrian Venture, powered by actor Vishakha Singh,[93] to launch an artificial intelligence based chat-bot for the production house through Facebook Messenger.

[94] Hema Rukmani had stated that "though we share the information about the film through the official Twitter handle of the production house, there must be false news prevailing all around.

[97] Few sources from the production house stated that "if one uses the term Mersal for commercial purposes, a part of their revenue should be paid to the team as royalty".

[118][119] The film was re-released again in March 2018, following the producer council's strike against digital service providers over the increase of Virtual Print Fee charges.

[120] Mersal was screened at Grand Rex, France, which is the largest cinema theatre in Europe, due to the high demand of the film.

It is available in digital streaming platforms through Netflix and ZEE5 (in Tamil), YouTube and Prime video (in Telugu), Sun NXT (in Kannada), and Hotstar (in Malayalam).

[132] At the Chennai city box office, the film collected ₹1.50 crore and became the highest opening day grosser, beating Ajith Kumar's Vivegam.

[146] Manoj Kumar R. of The Indian Express also gave three-and-a-half out of five stars stating "Atlee has not just exploited Vijay's stardom to deliver a flamboyant crowd-pleaser (which he did in Theri already) but has fleshed out an interesting script that plays up the best onscreen traits of the actor.

[151] Anupama Subramanian of Deccan Chronicle gave two-and-a-half out of five stars and added "Though the storyline is not new, Atlee cleverly uses the terrific screen presence of Vijay and presents it in an engaging way".

[153] Sreedhar Pillai of Firstpost called that "the perfect film for the larger-than-life image of its superstar Vijay, has something in it to satiate viewers with varied tastes", giving a rating of three out of five stars.

[154] The New Indian Express-based critic Daniel Thimmayya called the film as "ultimate commercial entertainer that rides on Vijay's solid performance and Atlee's slick storytelling".

[156] Poornima Murali of News18 called the film "as good in parts: during the evocative flashbacks"; but pointed out a few lame dialogues, logical contradictions and frequent song sequences.

[157] Vikram Venkateshwaran of The Quint wrote "It’s got three whole Vijays, with intersecting plot lines, great fight scenes and twelve murders, that will either squeeze your heart, or make you cheer along, all in the name of entertainment".

[159] Shyam Goutham, in his review for the magazine The Week wrote "through the film which is packaged with heavy drama and action sequences, Atlee tries to convey a message.

[163] The Tamil Film Producers Council strike from 6–13 October over double taxation row,[164] and the denial of NOC from Animal Welfare Board of India (AWBI)[165] were rumoured to affect the plans release; however, it was resolved later.

The social media propaganda loss of this film amounts to an approximate ₹60 crore,[178] with references citing Atlee asked a salary hike of more than 300% and exceeding the production budget.

[180] In November 2018, the Canada-based magician Raman Sharma, who worked in the project accused Thenandal Studios of non-payment of dues and slammed the company for their unprofessional behaviour.