He attended Mc Dowell High School in Millcreek Township.Monahan attended the Edinboro University of Pennsylvania, in Edinboro, Pennsylvania.Monahan began his musical career singing with cover band Rogues Gallery from 1988 to 1990.
After the dissolution of the band, he left Erie in late 1993 and moved to California, where he met Rob Hotchkiss.
While progressing from the SF coffeehouse circuit to the LA club scene, Monahan and Hotchkiss added Jimmy Stafford (guitar), Charlie Colin (bass), and Scott Underwood (drums) to their lineup, thus officially forming Train.
From 1994 to 2006, Monahan released four studio albums with Train.
In 2002, the band earned two Grammys, one of them for the song "Drops of Jupiter (Tell Me)", which was written by Monahan and inspired by his late mother, who had died of cancer.
Aside from his work with Train, Monahan also sang additional vocals on the song "Shimmer" with the band Fuel in 2001.
In November 2005, he appeared as a guest vocalist on VH1's Decades Rock Live, where he covered Cyndi Lauper's hit single "Time After Time".Later, he took part in Storytellers — The Doors: A Celebration, paying tribute to The Doors by performing "Love Me Two Times". Monahan released his first solo album, Last of Seven, on September 18, 2007 and began a nationwide tour supporting it.He followed that tour with a small, intimate acoustic tour, which inspired his Last of Seven Acoustic compilation, available via digital download only.His first solo single, "Her Eyes", made the top 10 of Billboard's Hot AC chart.The album's second single was "Two Ways to Say Goodbye." On Last of Seven, Monahan duets with folk rock musician Brandi Carlile, with special guest appearances by Richie Sambora and Graham Nash.Monahan worked with Guy Chambers to co-write two songs for Tina Turner's hits album, Tina! In 2009, Train returned to the studio with the album Save Me, San Francisco.