Sebu Simonian grew up in Los Angeles County. His family is involved in the Armenian community, while Simonian himself was an editorial assistant at the English Section of the Armenian daily Asbarez in the late 1990s. He graduated from Glendale High School. He is an alumnus of the California State University, Northridge, where he studied music. Simonian started his first band when he was 15.In 2004, Simonian (as lead singer and keyboardist) and Ryan Welker, guitarist and backing vocals, formed the rock band Aviatic. Simonian met Ryan Merchant in 2008 through Craigslist while searching for a job as a music producer. Initially, they worked as jingle writers and wrote songs for other bands. They formed the indie pop duo Capital Cities in 2010. In 2017, Simonian was featured on Armenian singer Sirusho's single "Vuy Aman".