Brett Dennen with Grace Potter and the Nocturnals

In 2004, Dennen released his first self-titled album, Brett Dennen. His second album, So Much More, including the singles "Ain't No Reason", "She's Mine" and "Darlin' Do Not Fear". Dennen also contributed a cover of "Private Life" to the 2006 tribute album Drink To Bones That Turn To Dust: A Toast To Oingo Boingo. Dennen's music has been featured in several television shows, including Roadtrip Nation on PBS, Grey's Anatomy, the House episode "Family", The Unit episode "Freefall", and the Scrubs episode "My No Good Reason".
In 2008, Dennen, along with Jason Mraz, contributed the song "Long Road to Forgiveness" to the Survival International charity album Songs for Survival. In late October, Hope for the Hopeless, Dennen's third album, was released on the Downtown/Dualtone partnership. The song "Ain't Gonna Lose You" was featured on Grey's Anatomy and topped the iTunes folk charts.