Devarajan performed his first classical concert at the age of 18. The first movie for which he composed music was Kaalam Maarunnu (1955). He teamed up with poet-lyricist Vayalar Ramavarma in Chathurangam in 1959. His third movie – and the second with Vayalar – Bharya (1962) became a huge hit and made them a popular combination. His music earned him pride of place among those who had strived to earn a dignified status for film songs. His collaborations with Vayalar produced the golden era of Malayalam film music. Devarajan is remembered by prominent singers in Malayalam like K. J. Yesudas and Jayachandran as their Godfather. He was much feared and respected by all musicians and singers of that period, for his sound knowledge in classical music. He was the one who used the maximum number of raagas in Malayalam film music. His music embraced different styles with the Carnatic and Hindusthani melody lines meeting folk idioms and Western harmony. Despite being a strong atheist, he composed devotional songs like "Harivarasanam", "Guruvayoor Ambalanadayil", "Chethi Mandaram Thulasi", and "Nithyavishudhayam Kanyamariyame", which are considered classics in that genre. The Vayalar-Devarajan combine proved the most successful team till the death of Vayalar in the mid 1970s. A complete work of Devarajan, Devageethikal, composed by himself, has released and the book is published by Authentic books. Devarajan died of a heart attack at his residence in Chennai on 15 March 2006 at the age of 81. He was cremated with state honours in Paravur, his hometown.