Brad attended the University of California at Berkeley. In the early 90s, Hargreaves played in the Wyatt Kildow Quartet. This experimental jazz ensemble played weekly at the Tropical Haight, a Haight-Ashbury nightclub in San Francisco. The club eventually evolved into the punk watering hole, Molotoff's, in the modern lower-Haight district. He went on to record records with jazz artists Vijay Iyer and Liberty Ellman before joining Third Eye Blind in 1995, during the recording of their first album. He joined the newly formed Year Long Disaster in 2004 who released their debut self-titled record in 2007 under the label Volcom Entertainment.
As well as playing in Third Eye Blind and Year Long Disaster, Hargreaves also performs in small clubs as a Drummer/DJ under the name 'JustBrad' where he plays drums to popular songs in a night club setting. Hargreaves was nominated best drummer at the California Music Awards in 2000.
In recent tours Hargreaves has been showcasing his musical talents; sometimes switching between the drum kit, piano, and also guitar.