Leon James became interested in music as a result of his father Noel James's involvement in the industry as A. R. Rahman's manager, and began piano lessons aged three. He played in a college band called Zinx alongside Anirudh Ravichander, with the pair remaining close friends. He is also currently a part of Project Yuj, a "neo-Carnatic funk" band alongside Aalap Raju, Prakash Hariharan and Jeoraj George and the team released an independent album in November 2014. Prior to making his debut as a composer, Leon has worked as a keyboardist for stage shows and film albums composed by Santhosh Narayanan, Anirudh Ravichander and Thaman. He made a breakthrough in the Tamil film industry after his work was spotted by Raghava Lawrence, who was working on his horror comedy film Kanchana 2 (2015). The film went on to become amongst the profitable ventures of the year, with Leon's work noticed by critics. Soon after the release of the film in April 2015, he teamed up with singer Andrea Jeremiah to record a song called "Ezhunthu Vaa" to promote female empowerment. The successful nature of his work in his first album prompted producer Elred Kumar to sign him up to work on the whole album for the political-thriller, Ko 2 (2015). The album featured vocals from Bollywood artistes Vishal Dadlani, Salim Merchant and Neeti Mohan, while Chinmayi and Leon James, himself, also recorded songs. Leon James also chose to introduce Harish Sivaramakrishnan from the Bangalore-based rock band Agam and London-based singer Inno Genga, for their first respective songs in the Tamil film industry.