Jelen was discovered by Joseph Janus of Fearless Management, who originally wanted to sign him as a model. Instead, Jelen handed him a demo, and shortly thereafter, he was signed to a label and released his debut album Give It All Away in May 2004, promoted by appearances on TRL, AOL Breakers and Rock the Vote. The album also debuted at No. 13 on the Top Internet Albums chart, No. 120 on the Billboard Comprehensive Albums chart and No. 113 on the Billboard 200 albums chart in the United States, making it eligible for the Top Heatseekers chart, a chart of artists who have never entered the top 100 of the Billboard 200. The album debuted at No. 1 on the Top Heatseekers chart.

Jelen met model Fern Palmer in a New York City night club on 6 January 2004. The couple married on 28 June 2009 in a private garden wedding in Palmer’s hometown of Cleveland, Georgia. Jelen and Palmer have one child together, a daughter named Tallulah Rose Jelen born in 2013. As of April 23, 2019, the couple is separated.

Following his debut album, Jelen left Maverick Records and independently released the EP Rejected through Fearless Management Records in 2005. He wrote and recorded a song for a compilation album for Tori Amos’ RAINN organization and joined the Natural Resources Defense Council (NRDC) and Wildlife Works. Jelen also appeared on the compilation album Breaking for the Holidays in 2006 with his self-produced cover of Joni Mitchell’s “River” through Breaking Records.

Jelen’s second full-length album, Ex-Sensitive, was released on 17 July 2007. The album, formerly titled East and Pulse, was produced by Linda Perry and mixed by Bill Bottrell.

Jelen’s music has been featured on the TV shows One Tree Hill, Smallville and Las Vegas, and was used to promote the Academy Award-nominated Finding Neverland starring Johnny Depp and Kate Winslet. “Come On” also features in the film Love Wrecked with Amanda Bynes and in 2007, the instrumental version of “Come On” was featured in a trailer for The Bucket List. His song, Where Do We Go also appeared in the film Fired Up. In 2013, Jelen’s single “Come On” was used in promotions for the film Monsters University.

In November 2018, Jelen completed a Ph.D program in Environmental Science at Rutgers University, successfully defending his dissertation titled, “The Evolution of Microbial Electron Transfer on Earth.”