In 1973, he dropped out of Colby College to pursue music professionally. He wrote to his mother at the time, saying, "I'm heading west. I know 200 songs now, and I figure if I keep learning more I should be all right."
He eventually moved to Boulder, Colorado in the 1970s and became part of the music scene there. In Colorado, he met guitarist/bassist Charles Sawtelle, banjoist Pete Wernick, and guitarist Mike Scap, with whom he formed Hot Rize in 1978. Mike Scap was soon replaced by Nick Forster on bass with Sawtelle moving to guitar. Over the next twelve years, the quartet earned recognition as one of America's most innovative and entertaining bluegrass bands. Never straying too far from a traditional sound, Hot Rize stood out with fresh harmony singing, Wernick's melodic banjo playing, and O'Brien's easy-going rhythmic drive.
To broaden their repertoire, the members of Hot Rize would often split their show with a set of classic and offbeat country and western music in the comic guise of Red Knuckles and the Trailblazers. The band would walk off stage, change clothes, and reappear as a different band (O'Brien assumed the mantle of "Red Knuckles"), with its own songs, fictional back story and odd costumes. Hot Rize was the International Bluegrass Music Association's first Entertainer of the Year in 1990, and in 1993, O'Brien took the IBMA's Male Vocalist of the Year honors.
In 1990, Hot Rize disbanded as a regular touring and recording band. However, after the death of guitarist Charles Sawtelle, in 2002 Hot Rize was joined by award winning guitarist Bryan Sutton and the band began to once again play limited engagements.
Duets with Mollie O'Brien
In 1984, O'Brien and his sister Mollie O'Brien reunited for a Mother's Day concert, and four years later recorded the duet album Take Me Back
. Chip Renner of AllMusic gave the album 4.5/5 stars, and called it "a masterpiece." In 1986 they began performing again as an Americana duo, and produced two more albums, Remember Me
(1992), and Away Out on the Mountain
(1994). All three records were released on Sugar Hill Records.
O'Brien, who had already recorded several albums without Hot Rize, embarked on a solo career. He briefly signed to RCA Records, recording an album with them called "Odd Man In", before being dropped. Sugar Hill Records eventually released the album, and O'Brien has not signed to a major since. In 1990, O'Brien also charted along with Kathy Mattea on the duet "The Battle Hymn of Love", which peaked at No. 9 on the Billboard
Hot Country Singles & Tracks charts.
In 2010, O'Brien featured prominently on Kris Drever's second solo album, Mark the Hard Earth
. He also produced at least one instructional video/DVD of mandolin and bouzouki instruments.