Vassar made his debut on the country music scene in the late 1990s, co-writing singles for several country artists, including Tim McGraw ("For a Little While", "My Next Thirty Years"), Jo Dee Messina ("Bye, Bye", "I'm Alright"), Collin Raye ("Little Red Rodeo"), and Alan Jackson ("Right on the Money").

In 1999, he was named by American Society of Composers, Authors, and Publishers (ASCAP) as Country Songwriter of the Year.

Starting in the late 1990s, Vassar began writing songs that were recorded by several country music artists.

[2] The song was the lead-off single to Vassar's self-titled debut album, which he co-produced with Byron Gallimore.

Shortly after that song peaked, Tim McGraw topped the charts with "My Next Thirty Years", which Vassar co-wrote.

In addition, the album earned a gold certification from the Recording Industry Association of America (RIAA) for shipping 500,000 copies.

Vassar also co-wrote the tracks "God Bless This Town" and "Live It Up" on Marshall Dyllon's late 2000 debut album Enjoy the Ride, in addition to co-producing them with Robert Byrne.

Released exclusively through Walmart stores, this song featured guest vocals from Kenny Chesney, Brooks & Dunn, Martina McBride, and Sara Evans.

[4] While "American Child" was climbing the charts, Arista tested another song written by Vassar, "This Is God".

The re-issue featured "This Is God" along with a cover of Huey Lewis and the News's "Workin' for a Livin'", with Dann Huff producing both recordings.

2 "Last Day of My Life", which Vassar was inspired to write after attending the funeral of his friend Robert Byrne, with whom he co-wrote his 2001 single "Rose Bouquet".

[5] The second and final single from Greatest Hits, "The Woman in My Life" (another song co-written by Vassar and his wife), reached No.

In March 2007, Vassar signed to Universal South Records,[6] which became part of Show Dog-Universal Music in December 2009.

2 on the country charts, and Vassar's first album for Universal South (Prayer of a Common Man) was released.

On November 15, 2016, Vassar announced via his Facebook page that his new album, American Soul would be released on December 2, 2016.

It features songs written over the past 20 years but never-before recorded and new music, including "This Is Where the End Starts", co-written with daughter, Haley Vassar.

Numerous hit songwriters collaborated with Vassar on the album, including Ross Copperman, John Rich, Don Sampson, and Charlie Black.

[8] On March 26, 2002, Vassar married Julie Wood, with whom he co-wrote his singles "That's When I Love You" and "The Woman in My Life".