Unnikrishnan was initiated into Carnatic music at age of 12 by Seshadri, Unnikrishnan. He was inspired by Sangita Kalanidhi Dr. S. Ramanathan. He attended a special workshop for six months on "Veena Dhanammal Bhani" under Sangeetha Kalanidhi T.Brinda and Sangeetha Kalanidhi Dr. T.Vishwa Nathan.
He is a national award-winning playback singer for his debut film songs "Ennavale Adi Ennavale" and "Uyirum Neeye". These songs were composed by A. R. Rahman, with whom Unni Krishnan gave most of his memorable songs.He was the first male playback singer to get national award for a Tamil song. He was one of the permanent judges in the reality television show AIRTEL Super Singer on Vijay TV in seasons (2006, 2008, 2010-2011, 2013, 2015-2016,2018) and 2008 Idea Star Singer on Asianet.
Unnikrishnan is also becoming known for his experimental work. In 2008, he presented a novel jazz concert in Thiruvananthapuram with the Eli Yamin Jazz Quartet and pianist Anil Srinivasan.
He prefers singing classical songs over pop music.
“Carnatic music has grown to a great extent. The taste of the audience has changed with time. Youngsters have developed a taste for the music form and the number of people flocking to these concerts has increased by leaps and bounds. There is novelty in the genre.”He got many awards like "Tamil Nadu's Kalaimamani","Nada Bhushanam","Isai Peroli","Yuva Kala Bharathi","Isayin Punnagai","Isai Selvam","Sangeetha Kalasarathy","Sangeetha Chakravarthy".
“The nuances of Carnatic music may be difficult for a layman to understand but music lovers today are willing to put in the effort to enjoy the music. I have seen youngsters talking about this form of music with enthusiasm. People take time off their busy schedules to come and listen to us artistes. So, it’s our responsibility to ensure that they enjoy the music. Even in reality shows, we ask the contestants to develop a taste for Carnatic music so that they can perform better in light music”.