It marks Mahendran's directorial debut and is partly based on Uma Chandran's novel of the same name, which was serialised in the Tamil magazine Kalki in 1966.

Mullum Malarum tells the story of Kali (Rajinikanth), a winch operator of a cable trolley who dotes on his sister Valli (Shoba) since they were orphaned, and clashes with his boss Kumaran (Sarath Babu).

Mahendran read only part of the novel, and developed the screenplay as he wanted, making a visually-focused film without formulaic Tamil cinema conventions he disliked such as melodrama, overacting, excessive dialogue and duets.

Since Mahendran had no previous directing experience, cinematographer Balu Mahendra, who was already an established director, assisted him with the screenplay, dialogue, camera angles, casting and editing.

Principal photography lasted for about 30 days, taking place primarily in Sringeri, Karnataka, though some scenes were also filmed in Ooty, Tamil Nadu.

Although it opened to tepid box-office earnings, positive reviews from critics and favourable word of mouth in later weeks helped make it a success with a theatrical run of over 100 days.

The film received praise primarily for Rajinikanth's performance, Balu Mahendra's cinematography, Ilaiyaraaja's music, Mahendran's writing and establishing Tamil cinema as a "visual medium".

The powerhouse's new divisional engineer, the rule-abiding but fair Kumaran, notices Kali offering free rides to unauthorised townspeople.

On a nearby canal's bank, Valli meets a young woman, Manga, who, along with her mother, has arrived from a drought-stricken town, Ilaiyangudi.

The next day, Manga convinces Kumaran and Valli to marry without Kali's knowledge, but he accosts their wedding party on its way to the temple.

It was only after Venu Chettiar of Ananthi Films approached Mahendran with an offer that he pitched Mullum Malarum, describing it as a brother and sister story.

[17][18] Mahendran was unable to find a worthy cinematographer until actor Kamal Haasan introduced him to Balu Mahendra, who agreed to work on the film, making his debut in Tamil cinema.

[22] Though Chettiar remonstrated against the actor's suitability for the role due to his dark skin and typecasting as a villain, he reluctantly capitulated after Mahendran intransigently declared that he could not possibly direct the film without him, believing him to be tailor-made for the part.

[26][27] It was shot primarily in Sringeri, Karnataka, with additional filming in Ooty, Tamil Nadu; principal photography lasted about 30 days.

[31] Mahendran also decided to characterise Manga (Jayalaxmi) as a "meen paithiyam" (meaning a "foodie who loves fish") after being inspired by Sringeri's marine environment.

[35] Sarath Babu was originally supposed to lip sync the full "Senthazham Poovil" scene, picturised on Kumaran and Valli, but Mahendra and Mahendran agreed on a montage after the actor performed a line or two.

[42] S. Rajanayagam, author of the 2015 book Popular Cinema and Politics in South India: The Films of MGR and Rajinikanth, described Kali as the thorn and flower in the film; he characterised Kali as an "angry young man with a kind heart" who does not admit mistakes, despite having committed acts such as breaking car headlights and allowing people to ride the trolley, in violation of the powerhouse's rules.

[44] Journalist Kavitha Muralidharan wrote that most of Mahendran's films show characters with contrasting personalities, citing the docile Valli and the garrulous Manga in Mullum Malarum as examples.

[45] According to film historian Yves Thoraval, Mullum Malarum explores "the extreme Oedipal possessiveness of a married brother for his younger sister".

Unlike Bairavi, the siblings in Mullum Malarum are not separated; this leads Kali's protectiveness of Valli to the brink of obsession.

[61] During its third or fourth week of release, positive magazine reviews and favourable word of mouth spread; Mullum Malarum became a commercial success, with a theatrical run of over 100 days.

[64] After watching the film and being impressed with Rajinikanth's performance, his mentor, director K. Balachander wrote in a letter of appreciation that he was proud to have introduced him as an actor in Tamil cinema.

[2][e] Mullum Malarum was well received at the time of its initial release, with commentators applauding it for establishing Tamil cinema as a "visual medium".

[64] The writer of a 25 August 1978 review in The Hindu appreciated the film for not having the "usual formula of fights, duets, intrigues and cabaret dances".

The reviewer further noted that Rajinikanth showed "his mature artistry in a portrayal of a turbulent illiterate worker with a blind passion for his sister".

The reviewer also praised the performances of Shoba and Jayalaxmi, called Balu Mahendra's camera work a "feast for the eyes", and Ilaiyaraaja's melodies "delicious".

[4] The Tamil magazine Ananda Vikatan, in its 3 September 1978 review, applauded the performances of Rajinikanth and Sarath Babu, along with Balu Mahendra's cinematography and Ilaiyaraaja's music.

The reviewer also praised Mahendran's filmmaking skills and the fact that he told the story in a sharp manner without long dialogues, likening the film to Kurinchi flowers due to their rarity and rating it 61 out of 100.

Ramachandran commented that the depiction of brother-sister relationships in film up to this point were full of dramatics, even in his own, but Mullum Malarum stood apart in its realism.

[82] The film's score has been regarded as one of the best of Ilaiyaraaja's career by commentators; the songs "Senthazham Poovil" and "Raman Aandalum" in particular, remain hugely popular.