Noted for his versatility in a variety of music genres,[1] KK is regarded among the greatest playback singers of India.

[3] KK began his career by singing advertising jingles and made his film debut in 1996 with a song in Maachis.

His most popular songs include — "Koi Kahe Kehta Rahe" from Dil Chahta Hai (2001), "O Humdum Suniyo Re" from Saathiya (2002), "Dola Re Dola" from Devdas (2002), "Uyirin Uyirae" from Kaaka Kaaka (2003), "Apadi Podu" from Ghilli (2004), "Dus Bahane" from Dus (2005), "Kya Mujhe Pyaar Hai" from Woh Lamhe... (2006), "Tu Hi Meri Shab Hai" from Gangster: A Love Story (2006), "Aankhon Mein Teri" from Om Shanti Om (2007), "Khuda Jane" from Bachna Ae Haseeno (2008), "Zara Sa" from Jannat (2008), "Sajde" from Khatta Meetha (2010), "Piya Aaye Na" from Aashiqui 2 (2013), "Mat Aazma Re" from Murder 3 (2013), "India Wale" from Happy New Year (2014), and "Tu Jo Mila" from Bajrangi Bhaijaan (2015).

[6][7] Born in Delhi on 23 August 1968 to Malayali parents, his mother, Kanakavalli of the Kunnath house and father, C. S. Menon.

He appeared in the song "Josh of India", released to support the Indian national team during the 1999 Cricket World Cup.

[11] After receiving a degree in commerce from Kirori Mal College, Kunnath spent six months as a marketing executive before pursuing his love of music.

[12] KK then became a playback singer, beginning with A. R. Rahman's "Kalluri Saaley" and "Hello Dr." from Kadir's Kadhal Desam and "Strawberry Kannae" from AVM Productions's 1997 musical film, Minsara Kanavu.

[17] Other popular songs included "Dola Re Dola" in Devdas (2002), "Kya Mujhe Pyaar Hai" in Woh Lamhe... (2006), "Aankhon Mein Teri" in Om Shanti Om (2007), "Khuda Jane" in Bachna Ae Haseeno (2008), "Piya Aaye Na" in Aashiqui 2 (2013), "Mat Aazma Re" in Murder 3 (2013), "India Wale" in Happy New Year (2014) and "Tu Jo Mila" from Bajrangi Bhaijaan (2015).

[18] In 2022, KK worked with filmmaker Srijit Mukherji and lyricist Gulzar on a song for Sherdil: The Pilibhit Saga.

[21] Despite his birth to a Malayali family in Thrissur, KK sang only one Malayalam song in his 25-year career: "Rahasyamay" in Puthiya Mukham (2009).

[25] Humsafar featured "Aasman Ke", "Dekho Na", "Yeh Kahan Mil Gaye Hum", "Rain Bhai Kaari (Maajhi)", and the English-language ballad "Cineraria".

[28] KK appeared on the MTV India musical programme Coke Studio,[29] singing the qawwali "Chadta Suraj" with the Sabri Brothers and a reprise of "Tu Aashiqui Hai" from Jhankaar Beats.

[32][33] On 29 August 2015, KK appeared in season two of the television singing-reality show Indian Idol Junior as a judge and guest jury member.

[34] In a 2019 Hindustan Times interview, KK said that he was active in the music industry with live performances and playback singing.

[42] Elaborating on his singing style, Ilina Acharya of Film Companion noted: "KK's smooth, honey-textured voice flowed like water.

On not taking any formal training, KK stated his idol as one of the reason and added, "From the beginning, I was able to learn a song by just hearing it, it is something that I’ve been blessed with.

"[44] Sneha Bengani from CNBC TV18 compared him to his inspiration and noted, "Much like Kumar’s, KK’s songs are standalone entities too, larger than the films or the albums they belong to.

"[53] Anupam Roy called KK his idol and added that he was a "livewire performer", who drew his energy from the crowd.

[54] Shaan praised KK's work ethics and added, "We had some of our best times while recording songs together or while performing on stage.

"[57] A. R. Rahman,[58] Richa Sharma,[59] Amit Mishra,[60] Usha Uthup,[61] Shreya Ghosal, Sonu Nigam, Vishal Dadlani and Mohit Chauhan have often praised his musical abilities and songs.

[70][71] His autopsy was videographed; the report cited myocardial infarction (heart attack) as the probable cause of death,[72] ruling out foul play.

According to the doctor who conducted the autopsy, KK could have survived if he had received cardiopulmonary resuscitation (CPR) immediately after losing consciousness.

[73] He had complained to his wife about pain in his shoulder and arm for several days before his death, thinking it was caused by digestive problems.

[citation needed] Three public interest litigations (PILs) related to the singer's death were registered in the Calcutta High Court.

[76] KK's remains were brought to Mumbai,[76] and his funeral was held at the Versova Hindu Cemetery on the following day (2 June).

In a Hindustan Times interview, KK was asked if he was bothered by being nominated for a number of awards but seldom winning.

[88] An article in The Hindu said, "Till the end, he remained a rage in the concert circuit and will be remembered as the singer who became the voice of the heart".

[89] Several singers like Arijit Singh, Shaan, Sunidhi Chauhan, Sonu Nigam, Shilpa Rao and others have given a tribute to KK, by singing his songs during their concerts.