At 19 he started a music band called Seven along with singers Franco Simon and Sangeeth. A Hindi pop band, they released an album 'Yeh Zindagani.'
Stephen, who started performing at a young age, has done the music arrangement for many films like Majaa, Thambi, Nammal, Azhagiya Thamizh Magan and Hariharan's album, Waqt Par Bolna.
Hariharan Pilla Happy Aanu was his maiden music directorial venture in Malayalam.
He is one of the regular band members in a band called Rex Band, a Christian contemporary band singing gospel fusion. He has had the opportunity to perform before Pope John Paul II. It was the only band from India. Stephen has orchestrated an instrumental version of the popular Rex Band melodies called ‘Different Vibes’.
In association with Kosmic Music, Stephen has also set to tune to a background of western music, Sanskrit slokas, mantras and verses from the Upanishads, called 'Sacred Chants of Kosmic Music,' and albums of holy chants on Ganesha, Shiva and Vishnu.
He has also assisted sarod maestro Amjad Ali Khan with his album on Christmas carols, 'Breaking Barriers.'
He has released his album Romanza which is a mix of world music, sprinkled with the flavour of real piano. Indian Ragaas have been treated with the rich use of contemporary piano. Hariharan, Ouseppachan and a Russian vocalist have appeared as guest artistes on the album.
Stephen’s solo stage shows have propelled him to the top league of on-stage performers.
Recently Stephen Devassy made his first appearance on a Tamil channel by playing for the contestants and playback singers Srinivas (singer), Chinmayi, Sujatha Mohan and Unnikrishnan in the unplugged round for the famous tamil reality music show "Airtel Super Singer". By performing in this show, the critically acclaimed artist has received the name and fame of the common crowd in Tamil Nadu as well.
Stephen is the record holder as Asia’s highest scorer in solo piano exams from Trinity School of Music, London with a score of 92.2%.
He also holds the record of completing the course in three years’ time.
Stephen has been felicitated with a vocational excellence award by the Rotary Club of Cochin Knights, Cochin.