Mani Ratnam was inspired by a Time magazine article about an American couple who took their daughter to Philippines to meet her biological mother for Kannathil Muthamittal.
The film also takes inspiration from a short story, Amuthavum Avanum by Sujatha Rangarajan
Like other Mani Ratnam projects, the film began production with very little official publicity in early 2001 with the media covering the project as either Manjal Kudai or Kudaigal.
The film was first reported as a continuum in the filmmaker's spectrum of films based on love and peace in the backdrop of war, after Roja (1992) , Bombay (1995) and Dil Se (1998).
The film was originally conceived as a taut racy thriller that centres on a script based on a female leader of a guerilla group.
After several rounds of discussion with co-writer Sujatha, Mani decided to base the film on human relationships in the backdrop of the Sri Lankan Civil War.
Kannathil Muthamittal was Madhavan's third straight Mani Ratnam project after Alaipayuthey and the Mani Ratnam production, Dumm Dumm Dumm.
For the role of Indira, Mani considered casting Rani Mukerji, Soundarya, Bhumika Chawla and Sneha, before finalising Simran to portray the character.
Madhavan and Simran then shot for two films simultaneously together, as they had also been cast in K Balachandar's Paarthale Paravasam as a married couple.
Nandita Das was roped in for the role of Shyama, making her debut in Tamil films, and in a later interview mentioned that the team shot for nearly thirteen hours a day.
Actress Sukanya dubbed for Nandita Das in the film.
Keerthana, the second daughter of actors Parthiban and Seetha, was cast as Amudha. Mani later revealed that she was his first choice even while scripting.
Mani Ratnam approached actor Vikram to make a special appearance as Keerthana's biological father, but his refusal meant that JD Chakravarthy was later handed the role.
The title is inspired by a famous phrase from a poem (Chinnanjiru Kiliye) written by poet Subramanya Bharathi.
Parts of the film shown to be Colombo in the film were shot in Puducherry.
Further schedules were carried out in the forests of Kerala to depict the base of the LTTE in northern Sri Lanka.
Simran's character was voiced by Deepa Venkat.
Actress Mounika lent her voice for Easwari Rao's character, while Thalaivasal Vijay spoke lines for Chakravarthy.
The male protagonist in the movie is a part-time author who writes under a female pen name. The dialogue writer for the movie, Sujatha, is also a male writing under a female pseudonym.
The film premiered at the 2002 Toronto International Film Festival, and was selected as India's official entry to the 2004 Cannes Film Festival.
The film also received a standing ovation, when screened at the San Francisco International Film Festival in 2003
The film went on to win six National Film Awards, three Filmfare Awards South, seven TN State Film Awards and Best Film awards at six international film festivals.
Sinhalese lyrics for the song Signore Signore were by B. H. Abdul Hameed.
The score and soundtrack fetched A. R. Rahman his fourth National Film Award for Best Music Direction.
Sreekar Prasad won best editing, Sridhar won best audiography, and Keerthana won best child actor in the National film awards that year.
The film won Audience Award - Best Feature Film at the Indian Film Festival of Los Angeles, 2003.
The film also won Best Picture at the Zimbabwe International Film Festival, 2003.
The film was dubbed in to Telugu as Amrutha and in Malayalam with the same title.
The film was dubbed in to Telugu as Amrutha and in Malayalam with the same title.
Kannathil Muthamittal got a release on Valentine's Day, stressing the importance of love and humanity.