Underwood was born in Woking, Surrey and attended the Winston Churchill School. He trained at the Karen Clarke Theatre Group (now Summerscales Performing Arts), was taught by vocal coach Phil Wisdom and attended Songtime Theatre Arts.
He moved to the United States in October 2006 where he studied at the American Musical and Dramatic Academy in New York. He graduated in February 2008.
He co-founded the Fundamental Theater Project in New York with Nicola Murphy in April 2010.
- Zero Hour
- The Last Keepers
- The Following
- Hello Again